Analytical methods for dating modern writing instrument inks on paper

Forensic Science International 197 (2010) 1–20

Review

Analytical methods for dating modern writing instrument inks on paper

Magdalena Ezcurra a,*, Juan M.G. Gongora a, Itxaso Maguregui b, Rosa Alonso a

a Analytical Chemistry Department, Faculty of Science and Technology, University of Basque Country (UPV-EHU), P.O. Box 644, 48080 Bilbao, Spainb Paint Department, Faculty of Fine Arts, University of Basque Country (UPV-EHU), P.O. Box. 644, 48080 Bilbao, Spain

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. Basic concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1. Closed and open systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2. Static and dynamic profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.3. Relative and absolute age. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.4. Mass invariance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3.1. Mitchell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3.2. Soderman and O’Connel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3.3. 1959, 1960, 1963—Kikuchi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3.4. Sen and Ghosh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4. Ball point pen ink dating. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.1. Composition of ball point pen inks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.2. Aging ink evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.3. Methods of ink age evaluation based on the evolution of resins over time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.3.1. 1980—Cantu and Brunelle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.3.2. 1987—Cantu and Prough . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.3.3. 1987, 1989—Brunelle, Breedlove, Midkiff and Brunelle, Lee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4.3.4. 1990—Isaacs and Clayton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4.3.5. 1993, 1994—Aginsky . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4.3.6. 1995—Brunelle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.3.7. 2005–2006 Kirsch, Weyermann, Koehler, Spengler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

A R T I C L E I N F O

Article history:

Received 6 March 2009

Received in revised form 16 November 2009

Accepted 18 November 2009

Available online 12 January 2010

Keywords:

Forensic science

Document examination

Questioned documents

Ink

Dating

Relative age

Absolute age

Ball point pen

Roller ball pen

Gel ink pen

A B S T R A C T

This work reviews the different analytical methods that have been proposed in the field of forensic dating

of inks from different modern writing instruments. The reported works have been classified according to

the writing instrument studied and the ink component analyzed in relation to aging. The study, done

chronologically, shows the advances experienced in the ink dating field in the last decades.

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M. Ezcurra et al. / Forensic Science International 197 (2010) 1–202

4.4. Methods of ink age evaluation based on the study of volatile compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.4.1. 1982—Stewart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.4.2. 1985—Humecki . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.4.3. 1988—Cantu. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.4.4. 1993, 1994, 1997 Aginsky . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4.4.5. 2000—Brazeau and Gaudreau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.4.6. 2002—Brazeau and Gaudreau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.4.7. 2004—Locicirio, Dujourdy, Mazzella, Margot, Lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.4.8. 2005—Bugler, Buchner and Dallmayer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.4.9. 2007—Weyermann, Kirsch, Costa Vera, Spengler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.4.10. 2008—Weyermann, Spengler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.5. Methods of ink aging evaluation based on the variations observed in the dyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.5.1. 1993, 1995—Aginsky . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.5.2. 2001—Lyter, McKeonwn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.5.3. 2001—Grim, Siegel, Allison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.5.4. 2001, 2002—Andrasko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.5.5. 2005—Andrasko, Kunicki . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.5.6. 2005—Siegel, Allison, Mohr, Dunn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.5.7. 2006—Weyermann, Kirsch, Costa-Vera, Spengler. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5. Gel ink dating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5.1. Composition of gel ink pens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5.2. Gel ink dating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5.2.1. Study of the degradation of blue gel ink dyes by IP-HPLC and electrospray sequential ionization–mass spectrometry (ESI-MS/MS) 16

5.2.2. Dating black ink strokes of roller ball and gel by GC and UV–vis spectrophotometry [56] . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.2.3. Classification and dating of black gel inks by Ion-Pairing High-Performance Liquid Chromatography (IP-HPLC) . . . . . . . . . 17

6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1. Introduction

Document dating and, therefore, the time that a document and/or ink could have been once placed on the paper, is one of the mostdifficult and hardest problems to solve in forensic science. This ismainly due to the great variety of inks that exist on the market, thecomplexity of chemical processes that inks undergo from the timethey are entered on the paper when they begin their aging processand the amount of external factors that can influence this agingprocess (environmental factors: light, humidity, temperature; inshort, storage conditions of the document) [1].

In spite of the complexity of the issue, important advances havebeen made with the single objective of determining for how longthe ink has been deposited on the paper, which would lead toestablishing the date on which the document was produced.

The modern writing instruments, Table 1 – those we can findnowadays in any store of any country and, therefore, those that aremost frequently used in questioned documents – are divided intotwo fundamental groups [2]:

1. Ball point pens: Containing oil-based inks and whose colorantsare dyes.

2. Non ball point pens: Containing water-based inks and whosecolorants are dyes as well as pigments (one, the other or both). Inthis second group fountain pens, roller ball pens, as well asmarkers and gel ink instruments are included.

Table 1Relevant introduction dates into the market in the field of ‘‘modern’’ writing

instruments.

Year Event

1945 Ball point pen.

1950 Glycols as inks’ solvents.

1955 Copper Phthalocianyne as a new dye in inks.

1963 Felt tip pens.

1967 Roller ball pens.

1970 Highlighters.

1984 Gel ink pens.

If a study of the ink-aging processes is intended, the elementsinvolved and the physical–chemical processes that these undergoafter depositing the ink on the paper, should also be known. In ageneral and simple manner, it is possible to say that the inks ofmanual writing instruments are composed of a colorant or mixtureof colorants, and a carrier or vehicle with one or several solventsand one or several resins [3].

– Colorants are divided into dyes (soluble in the vehicle and usedin viscous and fluid inks) and pigments (dispersed in the vehicleand used, in certain cases, in fluid inks in addition to dyes).

– The vehicle contains a solvent or mixture of them (fast dryingorganic solvents, water).

– One or several resins that contribute to the properties of theinks, such as the viscosity or adhesion of the ink to the paper.

– Other components are also added in a smaller proportion inorder to modify the rheological properties of inks. Theseadditives are usually kept secret by the manufacturing industry.

– In addition to this basic composition a chemical marker systemwhich is no longer in use because of its high cost, wasimplemented in the 70 s by the Office of Alcohol, Tobacco andFirearms of the American Treasury Department.

– Manufacturers included a tag (chemical marker as rare earthorganometallic compounds and traces of optical whiteners)[4–6] which did not vary over time, and another tag thatvaried yearly. The identification of one or both of thesemarkers can lead forensic scientists to define the earliestpossible date of the studied document. On the other hand, thislabeling system would undoubtedly imply the need forknowing which manufacturer used which chemical marker.

The aim of this work is to carry out a chronological review of thedifferent analytical methodologies used for ink dating. The reviewof papers and technical contributions on the professional meetingsbegins with the marketing of the first ball point pen back in 1945and goes on until nowadays.

Fig. 1. Desmethylation processes of methyl violet family.

M. Ezcurra et al. / Forensic Science International 197 (2010) 1–20 3

2. Basic concepts

2.1. Closed and open systems

To begin dealing with this subject it is necessary to define thefollowing terms: closed system, refers to the ink inside thewriting instrument reservoir, and open system, refers to the inkalready entered on the paper and subjected to environmentalconditions.

From the first studies on ink aging, it was assumed that these donot undergo considerable variations within the writing mediareservoir (closed system). The first study done with the purpose ofdetermining if this hypothesis was correct or if the ink degradedinside the instruments reservoir before making contact with paper,dates back to 2002 [7], and, making use of Laser Desorption–MassSpectrometry (LDMS). Authors concluded that most of the olderinstrument’s inks studied had not aged within the chambers, ashad been assumed until then. Nevertheless, the analysis of some ofthe ink samples did suggest some aging even within the cartridge.

In 2005, Andrasko and Kunicki [8] ran a new study on agingusing inks inside the ball point pen chambers. These authors foundthat there was no indication of aging in terms of changes in thecomposition of dyes within the chamber of a regularly used ballpoint pen, but detected considerable aging in inks near the tip inball point pen chambers that had not been used to write for severalyears. In this case they detected evaporation of the volatilecompounds (specifically phenoxyethanol), as well as the degrada-tion of the dye mixture. These facts were observed in the first threecentimeters of writing, with the exception of BIC brand ball pointpens for which it was observed during the first 50 centimeters.

2.2. Static and dynamic profiles

The static and dynamic profiles are established for opensystems, that is, inks that age outside the ball point pen reservoir,on a paper.

The static profile [2], defined as the analytical profile of an inkthat includes the stable properties of the same, that is, thoseproperties that do not undergo variations over time. Static profilesof inks are usually constituted by a registry of their opticalproperties and their thin-layer chromatogram which allowsestablishing the existence of the different colorants that composethe ink. The more detailed the profile is, the better degree ofdiscrimination between the inks shall be.

The static approach allows determining:

1. Whether an ink displays differences or not regarding itscomposition with another ink by comparing their static profiles.

2. The exclusion or the identification of a source for an ink bymatching its profile within the patterns profiles gathered in anink library. The larger an ink collection is, the more reliable thematch will be.

3. The date of first introduction of a given ink. If researchers haveaccess to a large data base of the various inks, their components,tags and year of manufacture (Ink Library [9]), they can delimitthe period of time in identifying an ink. The border of this periodwould always be the first year of introduction of the inkcommunicated by the manufacturers. As a result of this,detecting anachronisms, fraud can be detected.

Another concept to define is the dynamic profile [2], ananalytical profile of the ink that considers the processes andchanges that occur in the different components of the ink, once ithas been entered on the paper, hence beginning its contact withair, light and relative humidity. When an ink is entered on a paperthe following physical–chemical processes begin: degradation of

colorants, evaporation of solvents and hardening-polymerization of

the resins.

1. Degradation of colorants: Some of the most typically usedcolorants in the ink manufacturing industry for writinginstruments decompose gradually.

If photo unstable compounds exist in the inks composition,such as the methyl violet family, whenever the ink on the paperis exposed to light it will decompose, while sometimes evenappreciating, at first sight, a loss of color.

In the methyl violet family of dyes, the more methyl groupsthe compound contains the more intense the color is. Crystalviolet CV loses a methyl becoming methyl violet, which at thesame time loses another methyl group to give rise totetramethyl-p-rosaniline (TPR) (Fig. 1).

This decomposition even takes place in the dark, ought to theoxidative action of the oxygen in the air.

No variations in the solubility of the colorants are observedwith the passage of time.

2. Evaporation of solvents: The volatile compounds (solvents) of theink diminish over time. Most volatile components of the ink willevaporate in the first minutes, just after depositing the ink onthe paper. This initial loss will be of up to 90%, then the amountof evaporated components decreases and, after a period of time,which for ball point pens could be between 1 and 2 years, theamount of solvents present stabilizes. The time elapsed until thevolatile compounds stabilize is dependent on the ink formulaand its storage conditions.

3. Hardening-polymerization of the resins: The resins present in inksbegin to harden as soon as the ink is entered on the paper. Thesolidification or hardening of resins is a complex physical–chemical process that includes polymerization, a decrease ofintermolecular distances, crossed bonds, etc. When resinsharden their solubility diminishes but, what is more important,they trap the colorants and the volatile components in such away that, the longer the ink has been on the paper, the moredifficult it is to extract. This process has a limit, as it has beenobserved that the hardening of resins stabilizes in an interval ofbetween 8 months and 2 years.

In order to date an ink it will be necessary, therefore, toascertain a relation of these physical–chemical processes de-scribed with measurable and reproducible parameters. Theestablishment of the variation of these parameters over time willprovide the information needed for dating a given ink.

The dynamic approach allows distinguishing between inks thatonly differ on their age.

2.3. Relative and absolute age

Another two terms that are used in dating studies of ink withinthe frame of the dynamic profile are the relative and absolute age.[16]

Relative age: refers to establishing which of two inks with thesame formula placed on the same paper has been entered prior tothe other. This concept is used in the dynamic approach where, as itis said above, two inks that only differ on their age can becompared.

On the other hand the relative age concept involves sine qua non

conditions: ink samples being compared must have the same


formula, must be placed on the same paper and have to be keptunder the same storage conditions. The amount of the ink in all thesamples must be the same in all cases.

Absolute age: This is a practical concept introduced operation-ally by Aginsky [10] to estimate the age of the ink itself withoutrequiring the identification of the ink formula, nor a patterncomparison.

His proposal was to determine the rate at which an ink ages byheating a sample of the questioned ink and comparing this withanother sample of the same questioned ink that has not beenheated. Heating the ink sample induces an artificial aging of theink.

2.4. Mass invariance [16]

Since dating an ink always requires carrying out a compara-tive study, the amount of ink taken from the paper andthen tested should be the same, for all samples. Hence,the results cannot be influenced by the amount of inksampled.

But, even in the unlikely event of having, the same qualitystroke (same thickness, same pressure, same width, etc.), theamount of ink collected could be different if the sampling wouldbe repeated. Therefore, a methodology that ensures themeasurements are independent of the ink amount sampled(mass invariance) is needed. One solution to this problem istaking ratios. If two measurements depend linearly on theamount sampled, their ratio is independent on the amountsampled.

3. Background

The study of the dating of current inks has its embryo and originin the studies performed with iron-gall inks.

The studies of the dating of Iron Gallotanate inks, consider threedifferent kinds of test: ion migration test, color change test andsolubility test. Several investigations will be exposed.

3.1. Mitchell

Mitchell [11] proposes the extraction of iron-gall ink from thepaper when it is deposited with a reagent for its ulterior study.

Experimental procedure: Among the different reagents tested ashydrochloric acid (HCl), bromine water, hypochlorous acid andhydrogen peroxide, the author proposes a 5% solution of oxalicacid (C2O4H2) to apply a drop to one stroke of ink and study theamount of the diffusion, if any, of the blue pigment. It must betaken into account the speed of the reaction and the amount ofdiffusion.Findings: When an iron-gall ink is recently deposited on a paper,it rapidly reacts with oxalic acid. If this ink has been placed onthe paper for a year or so, it reacts slowly, and if it has been onthe paper for 6 or 10 years, it does not react with oxalic acid for along time.

3.2. Soderman and O’Connel

Soderman and O’Connel [12] referred for the first time aboutthe accelerated aging of an ink for the determination of its age. Thatconcept developed by Van Ledden Hulseboch from Holland,appears in their book ‘‘Modern Criminal Investigation’’. Likewise,they compare the ink that has not been aged with that which has;this comparative process being the one that will subsequently beused in present ink dating.

Experimental procedure: In their book, they proposecovering the whole document with a metallic sheet exceptfor one letter. Expose this letter to UV radiation for a quarterof an hour at a distance of 5 inches (12.7 cm) and laterstudy the ink exposed to radiation and that covered by themetal.Findings: If it results that the non-exposed dissolves in waterwith greater ease than the one exposed to radiation we can saythat the entry is recent. In case both equally dissolve, the testwould be non-conclusive.

It is true that they work with iron-gall inks, but it is equally truethat the concept of accelerated aging by exposure to UV radiationand the comparison of this exposed ink with the ink itself, withoutaccelerated aging, are introduced.

3.3. 1959, 1960, 1963—Kikuchi

Works by a pioneer woman in this field, Yukie Kikuchi [13–15]deserve a significant mention in this section. She examined thedispersion of an iron-gall ink in a spot test with oxalic acid, asMitchel’s works, considering that the greater time it takes intodissolution, the older the ink is, based in the fact that ink solubilitydecreases with age.

The differences from Mitchell’s work are mainly:

1. The concentration of oxalic acid reagent solution is between0.01% and 0.025% instead of 5% of Mitchell used.

2. Quantitative analyses: she measures the time to reach thebeginning of dissolution instead of Mitchell that gave a nonmeasurable result.

3. She introduces the measurement of the paper as a blank andtakes into account the error ranges margins.

4. Aging curves: She plots dissolution time (s) vs. elapsed time(months). Therefore, the time for dissolution to start is afunction of the ink’s age.

Experimental procedure: Drop an oxalic acid solution on the inkstroke and timed until the ink started to dissolve. Then measurethe dissolution rate under similar conditions.Findings: The relations between dissolution rate and time thewritings had been deposited on the paper (period of time) weredivided into four different categories with the followingresults: (1) for a period of time of few days, a very fastdissolution. (2) For a period of time of 6 months, fastdissolution but with small resistance. (3) For a period of timeof 5–6 years, rapid decrease in dissolution during the first fewmonths and after that more gradually dissolution. (4) For aperiod of time over 6–7 years.The error range margin for this work was 4 months in the firstand second period and about 3 years for the third period.

Subsequently, and as Cantu [16,17] exposes from hisprivate conversations with Kikuchi, this author was one ofthe pioneers first to develop an analysis for the dating ofball point inks. She expanded the application of her techniqueto ball point pen inks, measuring discoloration of the ink byadding a drop of diluted hydrochloric acid at one point of the inkstroke.

3.4. Sen and Ghosh

Sen and Ghosh [18] measured the changes in iron-base inkstrokes from a period of 28 years by thin layer chromatography(TLC) examination of the blue dye and iron content. They

Table 2Experimental methods developed by different authors and their contribution to the actual approaches in dating inks.

Year Author Experimental Methods Analytical measurement Contribution to the actual approaches

1920 Mitchell Extraction with 5% Oxalic acid solution. Qualitative

1935 Soderman and O’Conne Acceleration of the age of an ink by

UV and comparison with itself.

Accelerated aging ink

1959 Kikuchi Extraction with 0,01% Oxalic acid solution. Quantitative

1971 Sen and Ghosh TLC examination of inks. Ratio for mass invariance


introduced the idea of a ratio to achieve the mass invariance in themeasurements.

Experimental procedure: They extracted the inks with methanoland then spotted on the TLC plate. After that, they developedthe plates using a solvent system consisting of n-butanol–acetic acid–water (45:10:45). Blue spots with the same Rfvalues in all the chromatograms were found. The area of thoseblue spots, the main colored compound of the inks, wasscanned by means of a photodensitometer. After the separa-tion of dyestuffs, the paper of strokes was ignited at a lowtemperature to burn off the carbon, the ash was dissolved inHCl, a solution of ammonium thiocyanate and of amyl alcoholwas added and the result of this was spotted on a TLC plate andevaluated photodensitometrically. The invariance of mass wasachieved by doing the ratio between the first and the secondmeasurements.Findings: They found that the main dyestuff, deep blue spot, ofthe iron-base inks shows a linear decrease against the time forat least 28 years and this behavior is sufficient to specify the ageof the ink. And they also found another characteristic, as anoxidation product of a dye component, which appears at about3 months and disappears when the inks were around 9 yearsold. This fact can allow establishing the age of the ink.

The underlying ideas of these works that are still present in thenowadays researches are: (1) changes of the extent of extractionwith time, (2) comparison of one ink with itself when this has beensubmitted into an accelerating age process, (3) achievement ofmass independence by doing ratios. In Table 2, a summary ofdifferent experimental methods detailed above for dating ink iscollected.

4. Ball point pen ink dating

4.1. Composition of ball point pen inks

Most of the studies that have been done in the field of ink datinghave been carried out on ball point pens. The inks of theseinstruments are viscous and are insoluble in water. These inks arecomprised of colorants dissolved in one or several solvents andresins to which other components can be incorporated asadditives, in order to modify the properties of inks, such asviscosity adjusters, elasticity modifiers, corrosion inhibitors orlubricants for the sphere of the ball.

Resins are natural or synthetic substances of high molecularweight that are initially liquid and that little by little dry andharden. Among those currently used in ballpoint inks, Brunelle etal. [19] included alkyd resins, polyester resins, colophony resin,phenolic resins . . . and, later, Weyermann [20] pointed outchloride and polyvinyl acetate, oleylamine ethoxylate, phthalicacid ester, hydrogenated acetophenone, condensed formalde-hyde.

The solvents used at the beginning of these inks were oleine,castor oil, and mineral oil. In the 1950s glycols as solvents wereintroduced. The most widely used today in this ink group are

phenoxyethanol, phenoxyethoxyethanol, dipropylene glycol,phthalic anhydride, oleic acid, benzyl alcohol, 2-pyrrolidone,butylene glycol, among others [19,20].

The colorants used in writing inks can be the so-called dyes, orcolorants soluble in the vehicle and pigments or insolublecolorants. In ballpoint pen inks, soluble dyes that dissolve invehicle are used, among which stand out Victory Blue (VB);rhodamine B and 6G; the Methyl Violet group (pararosanilineswith four, five or six methyl group) made up by Crystal Violet (CV),Methyl Violet (MV), and tetramethyl-pararosanilines (TPR); andthe copper phthalocyanines introduced in the ink industry in 1954(Fig. 2).

The phatolocyanines shown in Fig. 2 are pigments. Thecopper phthalocianines dyes are produced by introducingsolubilizing groups such as one or more sulphonic acid functionsin CPC structure, e.g. CI solvents blue 38, amine salt of CPC usedin ball point pen inks, CI 48, amine salt of CPC, used inflexographic inks, CI direct blue 199, CPC derivative, used inwater based inks, and CI direct blue 86, CPC derivative also usedin water based inks.

4.2. Aging ink evaluation

The date on which an ink is entered on paper could becalculated if it were possible to track the behavior of one of itscomponents over time. From the revised bibliography three biglines of investigation can be carried out, taking into account thefollowing aspects:

1. The polymerization and hardness of resins: researches based onthe extent, simplicity and amount of ink extracted with asolvent. In this section the factor being considered is the rate ofdryness and hardening of resins, since the drier and harder theyare, more complexity will be observed in the extraction.

2. The loss of the solvents over time: The investigations that havestudied the behavior of ink volatile compounds (IVC) withrespect to time.

3. The degradation of dyes: The investigations in which degradationof current dyes in ballpoint inks has been monitored.

The processes suffered by the ink in the three cases areinterrelated but, in spite of this fact, and knowing the groups arenot watertight compartments, because they are overlap amongthem, the work have been divided following those criteria.

4.3. Methods of ink age evaluation based on the evolution of resins

over time

In this section the changes of extraction efficiencies over timeare studied. Mainly the extraction of dyes but also the extraction ofother non volatile and colorless components of inks is studied.

The efficiency of the extraction can be characterized by twoconcepts [21]:

1. The rate of the extraction: that is the speed the ink is extractedover time. They are two different parameters that characterizethe rate of extraction:

Fig. 2. Structure of different colorants used in ballpoint inks.



1.1. The R-ratio: the amount of ink extracted after a time, t1, as afraction of the amount of ink extracted after a longer periodof time, tf. Usually tf is the time after which no more ink canbe extracted from the paper. It is expected than R decreaseswith age.

1.2. The Lth extraction time, tL: The time it takes to extract L.When L is the amount of ink extracted from the paper. L

varies between 0 and 1. It is expected that tL increases withage.

2. The extent of the extraction: the amount of ink that can beextracted.2.1 The percent of extraction, P: The percent of an ink that can be

extracted just before no more ink can be extracted from thepaper. It is expected that P decreases with age.

4.3.1. 1980—Cantu and Brunelle

Kikutchi [15] was the first to measure the dissolution of aballpoint pen ink by doing a spot analysis on one point of theink stroke with diluted hydrochloric acid in order to determinethe ease with which it was extracted. Based on theseexperiments, in 1980 Cantu and Brunelle [16] present investiga-tions on the relative age of inks which they had been developingsince 1968 at the Bureau of Alcohol, Tobacco, Firearms andExplosives.

The extent of dye extraction with different solvents wasstudied. They no longer did it like Kikutchi on the same sheet ofpaper, but they introduced the innovation of taking samples fromthe document. They measured extractability, in outline, such as theoptical result of color density, introducing the use of spectroscopictechniques for measuring ample samples and densitometry forsmall samples.

The authors made a differentiation between the factors thatinfluence the extractability of the ink (E) dividing them in twomain groups: (1) The ink’s own factors (formula of the ink, type ofpaper on which it is deposited, amount of ink removed for analysis)and (2) Parameters of the extraction (solvent mixture used in theextraction, volume of the mixture, extraction time, etc.).

E ¼ EðFi; PeÞ

where E is the extractability of the ink, Fi the factors of the ink andPe are the parameters of extraction.

Experimental procedure: They used the mixture water:ethanol(1:1), as extractant for the same ink entered at differentmoments on the paper. With the purpose of quantifying ‘‘theextent of extraction’’ densitometer was used for small samples.Findings: They observed that the change of color for the oldest isweaker and also they noticed that there was a smaller degree ofextraction, whereas for most recent a fast change of color wasperceived, as well as a greater percentage of extraction. Theyalso observed that the drying process of ballpoint inks occursover a long period of time, 10 years had been studied. Theconclusion they arrived at and enunciate as a postulate is: ‘‘ifthere are two identical inks on a same support one older than the

other, the extractability of the oldest is smaller and slower than the

one of the most recent’’.

Once arrived at this point the ‘‘time’’ factor is introduced in thefollowing experimental procedure:

Experimental procedure: A plate of thin-layer chromatographywith stains obtained from the extraction at differentextraction times is spotted. Each sample will be more intensethan the previous one, since with more time it will be able toextract more amount of ink. If the density of color of thesepoints is moderate and they are put in an axis of coordinates

based on time, continuous curve extractabilities will beobtained.Findings: It is evident that if different amounts from the sameink are taken, they obtained different values, reason why it wasnecessary to look for a parameter independent of the amount ofink sampled. At the same time, to achieve this, it was necessaryto divide all the extractabilities at the different times betweenthe extractability at the time ‘‘t’’. This will give a parameter orratio that zero and one will vary between, and it will beindependent of the mass. This ratio will vary with the age of theink.

4.3.2. 1987—Cantu and Prough

In 1987 Cantu and Prough [22] developed and described in-depth the Solvent Extraction Technique to measure the relative ageof an ink. Before developing the method they put the limitationsthat the compared inks must have the same formula and mustappear on the same paper, or, in its defect, equal papers (of equalmanufacture) on different sheets, but with the same storageconditions.

The solvent extraction technique is supported on the measure-ment of the efficiency of the extraction based on one hand, on thepremise that the longer an ink has been deposited on the paperthe drier it will be and, therefore, the more difficult it will be toextract it or, what is the same, the efficiency of extraction will besmaller. The opposite, that is to say, the fresher the ink the easierit is extracted is also assumed as true. This approach is a proposalto make the extraction concept more quantitative by usinganalytical methods. The ‘‘effectiveness’’ of the extraction is goingto be measured so much by the rate as by the extent of theextraction, that is to say, how quickly and how much ink isextracted.

4.3.2.1. The rate of extraction. When an ink is extracted, theconcentration and color of the ink in the solvent being used asan extractant increase with time of extraction (t). Therepresentation of the variation of concentration over timeconstitutes an extraction curve, E(T,t), with T being the age of theink on paper and t the extraction time. That is, for each T (foreach age of the ink) it will be able to obtain a curve of dependentconcentration of the extraction time. It is evident that this curvewill become asymptotic for t =1, because in a determinedmoment the degree of extraction of the ink will be themaximum with that solvent.

The extraction curve can be achieved by measuring theabsorbance of the colored solutions. If the absorbance value ofthe solution at its maxima absorption wavelength is measured, acurve of extraction based on the time, t, will be obtained. In order tomeasure this absorbance one aliquot of the solvent at a givenmoment is applied on a TLC plate and the intensity of these resultsis measured by densitometry.

According to Beer’s law, each value of absorbance of anextraction curve is proportional to the concentration of the ink,which, as well, depends on the amount of sample ink. In order toavoid mass dependence a mass invariant extraction rate curve,X(T,t), can thus constructed from an extraction curve, E(T,t)normalizing it by its asymptotic value E(T,1). That is dividingeach of its absorbance values by the asymptote.

4.3.2.2. The extent of extraction. In the case of trying to compare theextent of the purpose of determining the relative age of the ink, itmust be independent of the mass. A way to achieve this is theprocedure of solvent sequential extraction technique, in which, afterthe first extraction with a weak solvent (weak solvent being thatwhich has poor extraction capacity of the ink, that is, it extractslittle ink or it extracts it slowly) one second extraction with a


strong solvent (all extracting solvent) is made. If both volumes ofextraction are the same then the absorption of the first extractiondivided by the sum of this absorption plus the absorption of thesecond extraction becomes the percentage of extraction of the inkfor a time t given in the first solvent P(T,t).

PðT; tÞ ¼ EðT; tÞEðT; tÞ þ E�ðT;1Þ � 100

where E(T,t) is the degree of extraction of the ink in the first solvent(weak solvent) after t minutes of extraction and E*(T,1) is thedegree of extraction of all the ink that was left remainder in theresiduum after the first extraction that is extracted with the second‘‘strong’’ solvent. P(T,t) represents the degree of extractionindependent of the mass.

On the other hand, an extraction curve is the summation of allthe individual extraction curves for each of the dyes:

EðT; tÞ ¼X

EiðT; tÞ

That is, when an aliquot is placed on a thin-layer chromatogra-phy plate originating from an extraction at a specific time, adensitometric value will be obtained. If development of thechromatogram is made, the dyes will separate thereby obtainingdifferent densitometric values for each one of the dyes.

Experimental procedure: On the experimental part, the authorspropose several methods, however they incline toward thin-layer chromatography densitometry: first, it is necessary totake a series of samples of the referenced paper (so that anaverage can soon be done) using a biopsy needle or a scalpel.These samples are placed in conical-shaped vials. At time zerot0,10 ml of solvent are added. Later, to obtain points of anextraction curve, it is necessary to remove aliquot parts fromthe solution of extraction at preselected times (t1 = 5 min,t2 = 10 min, . . ., tn = 30 min, being tn the time on which theextraction is almost complete) and measuring their color. Thismeasurement is indirectly taking by spotting each aliquot on aTLC plate (as, for example, a Merck silica gel withoutfluorescence indicator) and taking a densitometric measure-ment of the wavelength indirectly from its highest absorbance(for blue and black inks, the 580 nm value is the most suitable).At this point a plate with different spots will be able to be seen,each one of which has a higher intensity of color than theprevious.Findings: The solvent extraction technique distinguishes inkof the same formula written at different times on the samepaper.Ink of different age differ more in the extent of extraction, aspercent of extraction, than in their rate of extraction.The choice of the solvent is one of the key elements. Thestrength of the solvent is guided by the ability to discriminateage units, that is, days, weeks, months, years, etc.In this type of methodology the necessity of a statisticaltreatment is evident.

4.3.3. 1987, 1989—Brunelle, Breedlove, Midkiff and Brunelle, Lee

In the same year, 1987, Brunelle et al. [23] presents a work onthe relative dating of ballpoint inks, using the Single-Solvent

Extraction Technique. This procedure implies ink extraction withweak solvents, spotting the extracted sample on a thin-layerchromatography plate and measuring the amount of extracted inkdensitometrically. The difference between this method and theCantu’s Ratio method is that the amount of ink extracted ismeasuring directly without using ratios [24].

The age of the ink is compared with inks of well-known date,therefore, the limitation to the method is that it is dependent of the

mass and it requires identical amounts of the questioned ink andknowledge of the ink age.

With the purpose of surpassing this disadvantage Brunelle andLee [25] develop, in 1989, another method for dating ball pointpens, but this time it is independent of the mass. This reviewedprocedure is known as Dye Ratio Technique. The method wasdeveloped, as well, for two inks do not classified as ball point peninks.

They assumed that:

1. Ink components become less soluble in organic solvents as theink ages.

2. The subtle fading or degradation of the dyes is, also, a factor ofaging.

Experimental procedure: The technique consists of extractingthe ink either with a weak (n-butanol) or a strong solvent(pyridine). The extracted ink is spotted on a thin-layerchromatography plate and the dyes are separated using asolvent mixture of ethyl acetate:ethanol:water (70:35:30).After TLC development, the relative concentration of dyeswas measured scanning the dyes by a densitometer. All thepossible ratios were calculated.Findings: (1) Ratios of ink dyes separated by TLC vary with theage of the ink. (2) Some of the inks will continue aging forover 5 years. (3) For some inks, it was possible to estimate theage of ink up to 5 years after it was written. (4) Differentpaper causes different shaped ink aging curves.

4.3.4. 1990—Isaacs and Clayton

In 1990 Isaacs and Clayton [26] presented a work toassess the relative aging of ball point pen ink strokes madeby the same pens over a period of several months by extractingthe ink from the paper with polar solvents. Their approach wasan attempt to reduce the influence of the manipulative skill ofthe examiners in the Brunelle and Cantu methods. They used adiode array UV/vis spectrometer and they obtained extractioncurves.

Experimental procedure: Inks were deposited regularly onthe paper at intervals of two to three days for a period of4 months. Then, they extracted the paper microdots andplaced them at the inlet of the HPLC of the flow cell whencesolvents could be pumped through the paper directly into thecell. After that, measured by a spectrophotometer, theextraction characteristics of the individual dye componentsof the ink.Findings: Fresh ink marks tended to be more completelyextracted than older marks, nevertheless satisfactory resultsabout reliable indications of aging were not found.

4.3.5. 1993, 1994—Aginsky

In 1993, Aginsky [27,28], proposed four different ideas fordating ball point pen inks. At least in one of these proposals, resinsare clearly involved. He outlined a method of thin-layerchromatography to determine the changes with age of resinsand other nonvolatile, colorless compounds in ball point inks.These changes were detected by observing the results of the thin-layer chromatograms under UV light and can be evaluated usingscanning densitometry.

This is illustrated with the analysis of two components that ablue Parker ball point pen has, as well as two components of theRussian-made Soyuz blue-violet ball point pen which are fractionsof the resin phenoloformaldehyde and the verification that theirproportion equilibrates close to 3 years after the ink has beenentered on the paper.


Experimental procedure: Parker blue and Soyud blue-violet ballpoint inks were placed on the paper for a period of 6 years.Three steps were carried out for this purpose:First step: Extract the samples of the known ink (havingthe same formula of the questioned one) by a solvent andapplied onto a HPTLC plate with fluorescent indicator.Develop the plate by an able solvent to separate colorlesscomponents of the ink examined and to prevent overlappingthe zones of the colorless components and the components ofthe paper.

Observe the resulting chromatogram under UV illumination todetect the zones of colorless non-volatile components. Correla-tions between the content of two colorless components found andthe age of ink were established.

Second step: repeat the same procedure for the questioned ink.Third step: calculate the age of the questioned entry bycomparing the corresponding data obtained for the questionedand the known entries.Findings: For the Parker ink: The ratio substance A/substance Bgradually increases with the age, being minimum for the freshink and maximum for the 6 year old entry.

For the Soyuz ink: two different colorless components (C, D)were seen on the chromatogram. The relative proportions of thosecomponents, fractions of phenolformaldehyde resins, increaseswith the age, but it equilibrates after about a year and a half sincethe ink has been deposited on the paper.

4.3.6. 1995—Brunelle

Brunelle [29] in 1995 described a new method that comparestwo ink samples taken from the same entry with no need ofpatterns; one of them was heated to induce aging and the other oneremain unheated. In this case the four dyes from the family ofmethyl violet are taken into account. The analyzed ink was aFormulab 587 black ball point ink.

Experimental procedure: Two samples of the ink were taken.One of them was treated heating the sample at 100 8C for20 min, the other one remained untreated. Both of them wereextracted first by n-butanol for 12 min, secondly by pyridinefor 15 min.The TLC plate was developed, and only the four central bands ofthe TLC plate were tracked. The extent of extraction decreaseswith the time being the overall decrease 31% for the unheatedsample and 27% for the heated sample.If the four bands of methyl violet family are taken into accountthe overall 31% can be transformed into 3% + 11% + 11% + 6%,and the 27% into 3% + 10% + 9% + 5% (the percentages of eachdye are placed in the same position in the sum).Findings: they obtained a normalized extraction curve for eachband along the TLC plate. As it is already said the extents ofextraction in a weak solvent are more sensitive to aging thanthe rates of extraction.

Table 3Chronology of the different methods of dating inks by changes in the extractability of

Year Author M

1980 Cantu and Brunelle D

1987 Cantu and Prough So

1987 Brunelle Si

1988 Brunelle D

1990 Isaacs & Clayton So

1993 1995 Aginsky Brunelle TL

m

2005 Kirsch, Weyermann, Koehler, Spengler Re

ba

4.3.7. 2005–2006 Kirsch, Weyermann, Koehler, Spengler

After reviewing the diverse specialized scientific publicationson the subject, very few publications are found regarding inkdating based on the evolution of resins over time, and specifically,on the evolution of the rate and extent of the extraction of the dyes.The latest researches about resins deal with their polymerization.

Resins, ought to their strong molecular character, have beenless investigated so far. However, Kirsch et al. demonstrated thatdirect identification and quantification of the molecular compo-nents and their aging products by MALDI and/or ESI–MS could besuccesfully used to identify specific batches and to determine theirdate of production, as well as to detect the decomposition productsby thermal and photochemical aging processes. In addition toMALDI- and ESI–MS, High Resolution Fourier Transform IonCyclotron (FTICR) has been used in order to avoid complex MSspectra of resins [30–32].

In Table 3, a summary of the different methods described aboveare collected.

4.4. Methods of ink age evaluation based on the study of volatile

compounds

All the methods described below involve the loss of volatilecomponents of an ink after it has been deposited on the paper.Nevertheless, in many cases the role of the hardness of the resins isimportant as well.

With ink solvent, there are always two different processes thattake place at the same time: one is the volatilization of the IVCs andthe other is the hardening of the resins. Thus, an evaluation of theamount of a volatile component in t time implies both processes. Inthis sense, the option chosen in this work has been to include allthe methods that involve ink volatile components in this group,taking into account they are the pioneers’ ones.

4.4.1. 1982—Stewart

In the study of volatile compounds with the purpose of datingan ink entry on paper, Stewart [33] presented a pioneering study in1982. He found that the proportion of the ink volatile compounds(IVC) decreases over time since the ink is placed on the paper, bymonitoring IVC with a gas chromatography-flame ionizationdetector (GC/FID).

The procedure used is the following:

1. Identify the ink formula through thin-layer chromatography.2. Obtain this ink from the manufacturer or from the ink library.

Find the percentage of volatile compounds contained in thefresh ink, using GC-FID.

3. Place same-formulation ink samples on a sheet of paper ondifferent dates and storing them in standard file conditions.

4. Remove small samples from the previous sheet with a biopsyneedle and deposit them in sealed micro-vials.

5. Add from 10 to 15 ml of methanol through the cover of themicro-vial and place it in an ice bath for 5 min to slow down the

the ink dyes and colorless non volatile components (resins).

ethod

ifferent extent and extraction rate

lvent Extraction Method

ngle Solvent Extraction Technique

ye Ratio Technique

lvent extraction/Spectrophotometry

C for colorless, non-volatile compounds of inks, resolution under UV light Four

ethyl violet dyes Extractability

sins as new criteria for authenticating questioned documents and for dating of

ll point entries

Fig. 3. Structure of 2-phenoxyethanol.


propagation of methanol on its walls. An aliquot of between 5-10 ml is extracted to be injected into the gas chromatograph.

6. Detect and quantify the micro-amounts of the volatilecompounds by a GC/FID.

7. Obtain chromatograms and identify the peaks using the dataobtained from the ink manufacturer.

8. Plot an aging curve. This curve is achieved by finding twosufficiently resolute peaks to make a ratio. The ratio of Peak A/Peak B is tabulated versus to the age of the sample in days. Thisgives an aging curve for that particular ink formulation.

9. Analyze the questioned sample in the same way, and, obtain theratio of the area of both peaks. The previously calculated agecurve is used to determine the age of the questioned sample.This age would be absolute if, and only if, the storage conditionsof the questioned ink and that which is known were identical.

Nowhere throughout the cited article, are the volatilecompounds corresponding to the analyzed peaks A and B specified,however, in the bibliography below, so much LaPorte [39], asGaudreau-Brazeau [37] indicate phenoxyethanol (PE) (Fig. 3) asone of the volatile compounds to which Stewart refers. Thismethod has two clear limitations: first that the formula of theproblem ink needs to be identified and obtain information on itsvolatile compounds through the industry; second, the importanceof storage conditions of both inks. Known and questioned inkscannot differ if a comparison is intended.

4.4.2. 1985—Humecki

Three years later in 1985, Humecki [34] introduced FourierTransformed Infrared Spectroscopy (FTIR) for the study of thebehavior of ball point inks over time, measuring the decrease ofthe –OH band, what seems to be related with the loss of solvents asthe ink aging. This work consisted of taking a specific ink formulaand sample on a paper for a period of 22 years. Samples weredissolved in an ethanol: pyridine mixture (50:50), or just inpyridine. The extractions were measured in a spectrometer(Digilab FTS-20C) equipped with a triglycine sulphate (TGS)detector. Previously, a spectrum of the salt of the spectrometerwindow and the paper on which the ink had been deposited wereperformed as the blank verifying that, at least in this case, thepaper did not interfere since the spectrum was essentially thesame.

Comparing the IR spectra of the ink samples of different years,he observed that the O-H band located on the 3 mm decreased as anolder sample was analyzed.

An aging curve was constructed plotting the absorption ratioOH/CH (O–H band over the 3 mm and C–H band over the 3.4 mm)against to the age of the ink in years. That became asymptotic overthe 10 years. It is necessary to emphasize that the O–H band, whichprobably represents some volatile compounds, decreases morerapidly in the first years, and that later its diminution slows down.

Other ratio was also made taking into account the carbonylgroup band (C55O, over 5.8 mm) instead the OH band. Contrary towhat happens with OH band, the carbonyl band increases overtime, which would indicate an increase of some oxidized substanceof unknown identity. The measures obtained for this ratio areworse than for the previous one.

The studies by Humecki brought about an advance as far asevaluation techniques, as well as demonstrated the decrease of

solvents and increase of oxidation of an ink over time. As fordetermining factors, just to say that for its application, the sameway Humecki did, it is necessary to identify the questioned ink, andpossess an ink library in which this ink is stored and entered on apaper for a period of time 0 to 10 years in order to obtain the agecurve of the ink with the ratio OH/CH bands versus the time inyears.

4.4.3. 1988—Cantu

In 1988, Cantu [21] takes a qualitative step in the writing inkdating field introducing his work the ‘‘Comments on the Accelerated

Aging of ink’’ for the comparison of an ink to itself. In this sense healso establishes the aging parameters to produce an age curve withthe aim to determine if two curves (obtained under normal or atelevated temperatures conditions) can be related; so that, onecurve can predict the other. The great advance of this contributionis that it will not be necessary to know either the formula of thequestioned ink nor comparative patterns which are not alwaysavailable.

In this study, aging parameter that decrease monotonicallywith age were considered by Cantu, who developed variousapproaches to check several major theoretical hypothesis of inkaging using the percentage of extraction of a fluorescentrhodamine dye in a particular ink as aging property. He proposesthat the heating of this ink at 100 8C for 4 min would be equivalentto 3 months of natural aging at 20 8C of this ink.

This concept developed by Cantu, ‘‘accelerated aging of ink’’, canbe applied to any parameter that decreases monotonically with ageto estimate the age of an ink if there are not standards. Specifically,the accelerated aging of ink has been widely used to measure theloss of volatile compounds.

According Aginsky and other, the ink volatile compounds(IVC) of ball point inks level off between 2 and 3 years. If aquestioned ink is younger there will be differences betweenthe measurement of the volatile compounds of the non-heatedink and the measurements of the heated ink. If, on the contrary,the ink was older than 2 or 3 years, there would be nodifference in the measurements of the volatile compounds ofboth inks (heated or unheated) because of the stabilization ofthe IVC.

4.4.4. 1993, 1994, 1997 Aginsky

In 1993, Aginsky [27] developed two methods based on volatilecomponents; the first one was a combination of gas chromatogra-phy (GC) and spectrophotometric methods for determining themass ratio for ‘‘volatile compounds/dyes’’ of inks that decreaseswith their own age. The second was the use of GC to determine thereach of extraction of the volatile compounds of the inks thatdecreases when the ink ages on paper.

In these two approaches is necessary to know the formula ofquestioned ink and to obtain it from the manufacturers.

The first approach was based on measuring the amount of allavailable volatile components and of all dyes from the inkdeposited on the paper, and, on determining all relevant ratios(volatile/volatile, volatile/dye).

Experimental procedure: First of all, the questioned ink formulawas indentified using TLC and GC or GC/MS. And informationabout this ink is obtained from the manufacturers.Questioned ink, as well as known age ink (at different ages) wasremoved from the paper. All the volatile components wereseparated by GC obtaining their mass (m) by measuring the areaof their peaks. An internal standard was used. The ink wasextracted into a strong solvent as pyridine in order to obtain allthe dyes. The absorbance (A) measured at the absorptionmaximum of a dye was recorded.


If there were two different volatile components, X and Y, thefollowing ratios can be calculated:Ratio 1 = mx/my

Ratio 2 = mx/ARatio 3 = my/AFindings: The age of the questioned ink can be evaluated as amean value of the three results obtained above.

The second approach was the sequential solvent extraction

approach. It included the sequential extraction procedure withweak and strong solvent. Weak solvent extracts volatile compo-nents of an ink with the extent of extraction depending on the inkage. Strong solvent completely extracts the volatile components ofthe ink (with the same formula) fresh and old.

Experimental procedure: Volatile components were extractedinto a weak solvent and analyzed the extraction sample by GC;the mass of the volatile component is measured M1. Dry thesample and extract the remaining components into a strongsolvent and measure the mass M2. With those measurementscalculate the percent of extractions as the percent of the mass ofthe ink volatile components (%M) extracted in the weak solventrelative to its total amount contained in the analyzed sample.%M = [M1/(M1 + M2)] � 100. The %M is plotted versus the age,obtaining a percent extraction aging curve.Findings: Using a percent extraction aging curves the age of theQ entry analyzed can be determined.

Aginsky [28] in 1994 develops another different procedurefor ball point ink dating. This approach combines GC, todetermine the degree of extraction of an IVC, with theaccelerated aging technique. This procedure is very effectivewhen both entries being compared have been written indifferent moments with ball point pens of the same inkformulation that includes ingredients such as phenoxyethanolor phenoxyethoxyethanol and resins capable of polymerizingwhen the ink ages on the paper.

The great advantage that these methods contribute is thenonuse of dated patterns, that is, establishing the ink formula is notrequired and they do not require a reference sample of that sameink, instead the ink is compared to itself.

Experimental procedure: the procedure is the same than in theprevious approach. However, in this case, another sample istaken from the ink entry and heated moderately, at 80 8C for5 min, and analyzed as the same way. The percentageextraction value is calculated for the heated sample too. Bothof them, % of extraction for heated (%Mt) and unheated (%M)sample, are compared.Findings: If the difference between the percent of extraction forheated and unheated sample is:

a. less than 10%, it must be chosen another weak solvent.b. approximately 10% or larger it can be concluded the ink is fresh.c. if %M is>70% and the difference is>10%, it can be concluded the

ink analyzed is less than 6 months.

The method demonstrated to be useful in the cases that thegiven entry or signature was made after the time the investigationbegan.

Subsequently, Aginsky [10], in 1997, compared the Brunellemethod (4.3.6.) that analyzes dyes with his own methoddescribed above that analyzes the IVC, with the purpose ofevaluating which of the two methods is better. For this, sevendifferent ball point pens with blue and black inks, some freshand some old, were used. In this work Aginsky [60] reached the

conclusion that the studies of dyes are not as satisfactory as thestudies of the volatile compounds due mainly to three sources oferror:

The existence of dyes on the surface of the stroke that areeasily extracted with a weak solvent independently of the age ofthe ink.

The mass dependency in the method developed by Brunelle,instead of that in the Aginsky’s method, the obtained ratioeliminates the error source due to the mass dependency.

The error associated to densitometry measures taken of thespots on the thin-layer chromatography plate because the scancenters do not agree with the chromatographic spot centers.

4.4.5. 2000—Brazeau and Gaudreau

In the year 2000, a new study is presented by the CanadiansBrazeau, Gaudreau [35], published in 2007 [44], which shows thatthe volatile compounds of ball point inks can be quantified bydirect analysis on paper, implementing the Solid Phase Micro-extraction (SPME) technique prior to GC–MS.

A home-made sampling cell allows the non-destructive analysisof volatile compounds, using SPME. that does not require the use ofsolvents to extract analytes, it is used as the technique to monitorthe evaporation of the IVC as the ink ages on a document.

Andrasko [36] also reported in 2003 a SPME extraction of inkwith the purpose of dating.

4.4.6. 2002—Brazeau and Gaudreau

Brazeau and Gaudreau [37] present the approach used by theCanada Customs and Revenue Agency to determine the approxi-mate age of inks. This method is called Solvent Loss Ratio Method

(SLRM) and is included among the dynamic methods for ink dating.As its own name indicates it measures the evaporation of

solvents in the ink to achieve an approximation of the age of theink. This method is based on publications by Aginsky (1996) [38]and can be applied to determine if an ink that containsphenoxyethanol (PE) as a solvent has been entered on the paperin a period previous to a year since the analysis is performed.Phenoxyethanol was chosen as the most appropriate solvent afteranalyzing a sample of 63 ball point pens and discovering thatphenoxyethanol is one of the most common solvents in all thesamples analyzed. As in the Aginsky method, ink reference libraryis not required.

The basis of the method is that phenoxyethanol contained in anink evaporates at great speed in the first 6–8 months from theapplication of the ink on the paper. The rate of evaporation levelsoff in a period that goes from 6 to 18 months. Last, the evaporationof phenoxyethanol stops being significant after a period ofapproximately 2 years. This dynamic process is, precisely, theone used in this method for measuring the approximate age of theink.

Experimental procedure: The method consists of extracting twosets of ink samples (10 discs 1 mm Ø with 15 ml acetonitrilecontaining an internal standard as cresol). One of them will ageartificially by heating the set at 70 8C for 120 min, whereas theother will remain in the conditions in which it has beenextracted.The amount of phenoxyethanol of each set of samples isdetermined using a gas chromatograph coupled to massspectrometry (GC–MS), (measurements are taken and anaverage is made).Findings: The amount of PE that an ‘‘old’’ ink loses will be lessthan that lost by a ‘‘fresh’’ ink; for the simple reason that since itis older the loss of solvent velocity has decreased.On the other hand, if both sets of samples are comparedfrom the other it is obtained, if in the 120 min (Dt) the set of

Fig. 4. The amount of volatile components that evaporates during a natural or

accelerated aging process.


non-heated ink samples goes from having a ta age to having a(ta + Dt) age and an amount of phenoxyethanol [PE]a to[PE]a+Dt; the same heated ink will have changed from havinga ta age to a t1 age and an amount of phenoxyethanol [PE]a to[PE]1, Fig. 4.The solvent loss ratio (SLR) can be calculated the following way:R(%) = [(unheated ink � heated ink)/unheated ink] � 100.The age of the ink entered on the paper will therefore depend on%R, since this value will give the loss of solvent. A clear markerof the %R for each phase of the solvent evaporation, includingthe experimental error, should be established. The last point inwhich the curve %R can be�50 is established at 150 days; whichallows establishing that for values greater or equal to 50 the inkwill have been entered on the paper in the 150 days precedingthe completion of the analysis. The last point in which the curve%R can be �25 is established at 300 days. This allowsestablishing that for values greater than 25, the ink has beenentered on the paper in the 300 days prior to carrying out theanalysis and, finally, that after 300 days the %R values are lessthan 25.

In 2004 LaPorte et al. [39] attempt to determine the frequencywith which phenoxyethanol is found in ink formulae. For this, theauthors analyze the inks of 633 ball point pens using GC/MS.Phenoxyethanol was identified in 85% of black inks and 83% of blueinks.

4.4.7. 2004—Locicirio, Dujourdy, Mazzella, Margot, Lock

Lociciro et al. [40] extracted ink from the paper by a solvent andthen analyzing this ink by gas chromatography–mass spectrome-try (GC–MS). They determined the solvent content in the sampleand related it to the amount of an unidentified ink compound,which was observed to be stable in time.

Experimental Procedure: one cm of the ink stroke were extractedfrom the paper with a scalpel and then cut into smaller pieces.PE was extracted from ink samples and submited to aderivatization process using a mixture of chloroform/pyri-dine/MSTFA (5:5:1) for its subsequent quantification by GC–MS. 2 ml of the extracts were injected into a GC, two unknownsubstances were chosen as the stable compounds. Thesecompounds were quantified and used to calculate theevaporating compound-to-stable compound ratios.Findings: No correlation was found between the abovementioned ratios and the age of the inks. So, they concluded,ink dating is impossible using this approach, as the decrease

in solvent content was smaller than the error of quantifica-tion.

4.4.8. 2005—Bugler, Buchner and Dallmayer

In 2005, Bugler, Buchner and Dallmayer [41,42] describe theapplication of thermal desorption followed by GC–MS analysisfor dating ball point pen inks. The method uses a thermaldesorption technique in two stages of the ink sample on paperwhich is explained below. The proportion of the amount ofvolatile compounds found with a desorption at a low tempera-ture, as opposed to the amount of the volatile compounds foundat a high temperature, is established as the determination of theink age of the stroke being studied. This approach proposes amethod independent of the amount of ink sampled and thatavoids any contamination caused by the sample treatment.

These authors maintain that the methods applied until now, inwhich a ratio is made between the amounts of phenoxyethanolfound in two samples of the same ink, one without treating andanother heated, may have significant error due to possiblevariations in the two samples removed from the same ink. Theirmethod only involves one sample which is then heated at twodifferent temperatures.

With respect to how the ink behaved on paper, based, in the firstplace, on the amount of the PE that ball point inks initially containbetween 30 and 140 ng/mm, they verified that when depositingthe ink on paper 95% of PE was lost in the 3 first days, that after this,the PE decreases insignificantly but permanently and after that theamount of PE, trapped in the matrix ink resin/paper, remainsconstant and can be identified in insignificant amounts even in 50-year old samples.

The PE quantification was performance using an internal and/orexternal standard to make accurate measurements in thedescribed procedures. The limit of quantitation (LOQ = mean ofblank measurements + 10 � standard deviation of blank measure-ments) was 1 ng. And, the limit of detection (LOD = mean of blankmeasurements + 3 � standard deviation of blank measurements)was 0.4 ng.

Experimental Procedure: Three steps: (1) A sample of ink onpaper is heated at a T1 = 70 8C for 20 min. The evaporatedsolvent is collected and quantified (M1). (2) The same sample isheated at T2 = 200 8C for a period of 5 min. The evaporatedsolvent is quantified (M2). (3) The ratio V = M1/(M1 + M2) � 100is calculated.Findings: The ratio ‘‘V’’ between the amounts of PE obtained atlow temperature as opposed to the total amount of PE obtainedin both steps is a direct evaluation measurement/calculationof the age of the ball point ink. It is mass independent but itdepends on the type of the paper. They found three differentkinds of inks depending on its behavior: 38.5% of the inks havenot a detectable amount of solvent (PE) evaporated at 70 8C,25% of the inks are fast aging inks, that means their V decreasesbelow 10% within 2 weeks and staying on the same level forthe following 20 months, 36.5% of the inks are slowly aging

inks, their V ratios are high for fresh samples, but decreasewithin the test period values below 10%. The method isapplicable to slowly aging ball point pen inks with an age of upto 1.5 years.

From the study, general rules were deduced to determine theage of an unknown ink sample, of which we do not have a known-age curve. If V is greater than 20%, the ink that is being investigatedhas an age of less than 30 months. The values between 15% and 10%indicate that the ink is between 15 and 9 months, respectively.Since there are numerous ball point inks that give V values below5% even at the age of 1 month, if a V value of 5% or less is obtained, it

Fig. 5. Diphenylmethane derivatives Michler’s Ketone and Phenol formed as

products of the oxidation of Crystal Violet family dyes.

Table 4Chronology of ink aging evaluation methods based on the study of volatile compounds of inks.

Year Author Method

1982 Stewart GC/FID

1985 Humecki Infrared Spectroscopy - FTIR

1988 Cantu Accelerated ink aging to compare one ink to itself

1993, 2000 Aginsky Brazeau, Gaudreau GC/spectrophotometric methods ratio volatile compounds/dyes GC decrease of

volatile compounds Solid Phase Microextraction + GC/MS

2002 Brazeau, Gaudreau GC/MS + accelerated aging

2003 Andrasko Solid Phase Microextraction + GC/MS

2004 La Porte et al. PE incidence in ink formulas

2004 Locicirio, Mazzella, Dujourdy, Lock, Margot Quantification of PE by GC/MS

2005 Bugler, Buchner, Dallmayer Thermal Desorption in two phases + GC/MS

2007 Weyermann GC/MS variation of PE over time in laboratory conditions.

2008 Weyermann, Spengler Modelling of natural aging curves based on artificial aging curves


is not possible to conclude that the ink is old. In fact, a practical rulefor real cases is that if V gives less than 10%, the test is inconclusivebecause the method is not reliable in these cases. On the otherhand, the authors concluded that the proposed method depends onthe type of paper with the standard offices paper (80 g/m2)resulting in the highest values V.

4.4.9. 2007—Weyermann, Kirsch, Costa Vera, Spengler

Weyermann et al. [43] develop a method in whichsplitless gas chromatography-mass spectroscopy in selectedion mode for the quantitative analysis of solvents after liquidextraction with dichloromethane (DCM) containing 1,3-benzo-dioxole-5-methanol as internal standard (IS). Also the dryingmechanism of ball point pen ink on paper was quantitativelycharacterized by measuring how the solvent of an ink strokedisappears over time; both an evaporation and diffusion processare considered.

Experimental procedure: Extraction of solvents from the entrieswas made with DCM containing IS in a ultra-sonic bath during10 min. The extraction sample was injected to the GC/MS for itsdetection and quantification in the TIC mode. 15 particular ionswere selected and monitoring in the SIM mode. Quantificationwas performed by calculation the relative peak area (RPA) asfollows:

RPA ¼ Asi=AIS

where Asi is the solvent peak area and AIS the peak of internal

standardFindings: under laboratory storage conditions, it is possible thedifferentiation between fresh ink (<2 weeks on the paper) andolder inks. In real cases phenoxyethanol can migrate from onesheet of paper to another when they are stored successively, asin a book or a notebook, therefore, more parameters have to bestudied.

4.4.10. 2008—Weyermann, Spengler

In many of commented approaches, questioned documents ortheir inks have been exposed to high temperature (as well as tolight) to accelerate their aging process in order to simulate anartificial aging and reproduce their aging curves.

However, in a natural aging process, a document might beexposed to a variety of different conditions such as air flow,humidity, light, heat, . . ., completely different from those used inthe simulation in the laboratory. The modeling of natural aging ofdyes and solvents from ball point inks, proved to be very complex,because of the initial ink composition, the paper substrate and thestorage conditions. These factors must be taken into account in anyattempt to compare artificial aging to natural aging. According toWeyermann and Spengler [1], no accelerated aging model can be

standardized for all inks since these are stored under differentconditions and on different papers.

Despite of this fact, a mathematical transformation of artificialaging curves into modeled natural aging curves was developed byWeyermann and Spengler [1] with a specific ink composition on acertain type of paper substrate stored in controlled conditions. Thismathematical model could provide a good simulation, especiallyfor solvents. Reproducing environmental conditions prove to betoo complex in most cases.

In Table 4, an analytical methods list reported based on thestudy of volatile compounds of inks are given.

4.5. Methods of ink aging evaluation based on the variations observed

in the dyes

All the methods describe below involve the evolution of thecolored components of the ball point pen inks over time.

4.5.1. 1993, 1995—Aginsky

In 1993 Aginsky [27] develops a method of microspectropho-tometric determination of the color change velocity of inks as aresult of the reaction with strong organic bases such asbenzylamine or piperidine. This method follows work by TamaraSaphronenko [27] who used aqueous spot tests to distinguish theage of fountain pen inks, work that is based on what Mitchell [11]had done.

The same year, Aginsky [45] at the meeting of the InternationalAssociation of Forensic Sciences in Dusseldorf presents the resultsof his study on the aging of CV (Crystal Violet) and MV (Methylviolet), two of the dyes that are normally used in blue, violet andblack writing inks. These dyes are not stable and decompose withlight, but if they are not exposed to light and are kept in darkfolders they will undergo no changes. However, Aginsky demon-strated that these dyes, even in the dark, undergo an oxidativeprocess with the oxygen in the air, forming diphenylmethanederivatives (Michler’s ketone) and Phenol (Fig. 5). In any case, therewas no correlation between the concentration of Michler’s ketoneof inks and their age.


In 1995, Aginsky [46] publishes a non-destructive methodbased on microspectrophotometry to consider the relative age ofballpoint inks denominated the Proportion of Dyes Method. Themethod consists of determining the proportions of stable tounstable dyes from the superficial layer of the questioned inkstroke and from the whole ink film by comparing the reflectancevalues measured with natural light (specular reflectance) and withpolarized light (diffused reflectance) respectively. Examinationsusing polarized light involves using a cross polarizer to eliminatethe shine/brightness from the surface of the ink.

The older ink is the one that has less proportion of unstable tostable dyes on the top layer of the ink. That is to say, the ideaunderlying this method consists on when an ink ages the greaterchanges take place on the superficial layers of inks that are incontact with the environment. At the surface, the unstable dyeundergoes more change than stable dye (thus, their ratio goesdown with age).

Experimental Procedure: It was considered that the majority ofblue, violet and black ball point pen inks contain two dyes, onevery stable, as is phthalocyanine copper (D1) and another, verylittle stable, as is MV or CV (D2).For each ink stroke, eight points were taken that had similarthickness, similar superficial characteristics and homogeneityin the distribution of the ink. These points were located underthe microscope with polarized light (with the polarizer andanalyzer crossed) and recorded the reflectance spectrum withpolarized light (‘‘dif’’ series, diffused reflectance) and with non-polarized natural light (‘‘spec’’ series, specular reflactance).For each series, two wavelengths l1 and l2 were chosen for D1

(phthalocyanine copper: l1dif = 685 nm, l1

spec = 670 nm) andfor D2 (methyl violet: l2

dif = 615 nm and l2spec = 670 nm).

Afterwards, for each point analyzed, the value of the ratio, Zi, isfound. This is the ratio of the relatively unstable dye to thestable dye on the surface layer of the ink. It is given by:

Zi ¼ðZdif ÞiðZspecÞi

where (Zdif)i = {R(l1dif)i� C}/R(l2

dif)i and (Zspec)i = {R(l1spec)i� K}/

R(l2spec)i

‘‘i’’ is the index of the point; and C and K are specific coefficientsusing an iterative technique.Say that for ink line examined, the average or median of Z1 to Z8

is computed along with the dispersion (e.g. error bar) and thatthe method gives rather large error bars.Findings: The aging parameter (specular reflectance ratio/diffuse reflectance ratio) gradually decreased with age duringa 6 year-period.It is important to observe that no signal to reach a point ofleveling off was appraised in a period of 6 years.

In this case it is very important to consider that the changes thatnon-stable dyes (by successive loss of methyl groups) suffer arecaused by light, not by temperature and that documents kept in thedark will undergo less dye degradation than those exposed to light.Therefore, storage conditions are a very important variable in thisapproach.

This proposal is a non-destructive method. Nevertheless thetechnique must be performed efficiently in order to decrease thedistributional error in the reflectance measured areas of ink linesdue to inherently irregular distribution of ink per area.

4.5.2. 2001—Lyter, McKeonwn

At the Annual Meeting of the American Academy of ForensicSciences that took place in Seattle, Washington, in 2001, Lyter and

McKeonwn [47] developed a new GC method using Time-of-FlightSecondary Ion Mass Spectrometry (TOF-SIMS) technique for theDating of Writing Ink. Measurements of the possible chemicalchanges that ink undergoes when it ages were recorded by TOF-SIMS technique. They examined natural and artificially agedwritings of a single ink and found that ‘‘the method used coulddistinguish writings of different dates through the presence ofdifferent proportions of dye ions present in inks’’.

4.5.3. 2001—Grim, Siegel, Allison

In 2001, Grim et al. [48,49], published a study about the cationicdye Methyl Violet 2B, and the anionic dye, Solvent Black. Theystudied those two dyes by laser desorption–mass spectrometry(LD/MS) to provide molecular information and, also, theirdegradation products information. When the ink on the papersuffers an accelerated aging using UV irradiation, dye degradationproducts were formed and those products were detected using LD/MS. They measured ratios of the dyes molecules and thedegradation products and those ratios reflect the age of the ink.

4.5.4. 2001, 2002—Andrasko

In 2001, and the following year 2002, two studies by Andrasko[50,51] were published, both about the changes in the compositionof ball point inks, first, of inks stored in different lighting conditionsand, second, inks aged in the dark. The changes reviewed arelimited to dyes which compose the inks. In these studies HPLC withDiode Array Detection (DAD) at 540 nm was employed tomonitored changes in the chemical composition of the dyes.

The first makes reference to the changes revealed in dyes thatcompose ball point inks exposed to daylight and artificialfluorescent lights. The tracked dyes, Crystal Violet, CV, MethylViolet, MV and Tetra para-Rosaniline, TPR, are usually found ascations in the studied inks at pH values in which the work is done.The sample treatment consists on remove single written asteriskfrom the paper. The ink material was extracted with 0.2 ml ofmethanol for 30 min at room temperature followed by heating thevial content at boiling point for 1–2 min. After that the extract wasevaporated to dryness by stream of nitrogen and the dry residuewas dissolved in methanol, during the whole extraction procedurethe ink and the extract were kept in darkness or protected from theexposure to intense light.

On the other hand, these three dyes have poor resistance to lightand so much CV as MV decompose in daylight. This decompositionimplies a successive loss of methyl groups that are replaced byhydrogens, that is, CV decomposes in MV and MV in TPR, whereasTPR decomposes in other similar substances due to the gradual lossof the methyl groups. The changes of composition of CV, MV andTPR are illustrated in ternary diagrams. These three compounds arerelated among each other in such a way that the sum of the area ofthe three peaks detected at 540 nm is 100%, without consideringthe presence and concentration of other compounds.

In Fig. 6 a ternary diagram of six different inks put underdifferent light conditions is presented.

In it, the arrows mark the initial composition of the fresh inks,without exposing to light. The H2, H0 and B6 inks were exposed todaylight in the laboratory, that is, the inks were kept in thelaboratory and samples were taken for analysis in intervals of tendays. The V1 and GA inks were exposed to fluorescent light at adistance of about 5–10 cm. The samples for analysis were taken intwo-hour intervals. The points ^ and ^ represent the compositionof the inks H0 and H2 exposed to fluorescent light for 4 h. Thechanges of the L7 ink are due to normal aging of the ink, thesampling has been carried out in 1 year intervals, for a period of 3years.

For the H2 ink, we can gather that four hours exposure tofluorescent light ages more than ten days exposed to environmen-

Fig. 6. Ternary diagram of composition changes of CV, MV, and TPR and the different

light conditions presented by Andrasko in his mentioned paper.

Table 5Characteristic ions (m/z) obtained for MV and EV from mass spectra.

Dye m/z (u)

MV 358.1 344.1 330.1 316.1 302.0 288.0

EV 428.2 400.2 372.2 344.1 316.1 288.0


tal light within the laboratory (which initially has a percentage of60% CV; 36% MV and 4% TPR) and almost twenty days exposure tothe environmental light of the laboratory for the H0 ink (whichinitially presents percentages of 49% CV, 40% MV and 11% TPR).

The conclusions of Andrasko’s study are that it is not alwayseasy to state that two ink entries from different documents aredifferent at any time, a small exposure to daylight causes theoptical (color, infrared luminescence) and chemical properties tovary with changes like the one previously tracked CV!MV! TPR.The changes can be seen in the tertiary diagrams. These changescan determine the age for same inks entered on the same paper.

In his second study, published in the 2002, Andrasko [51]studied the chemical changes suffered by compounds kept in thedark, concluding that they were similar to those obtained in inksexposed to light or heat, but much slower. As in the previous case,ink aging was monitored through ternary diagrams that combinedthe dyes CV, MV, TPR and Victoria Blue (VB), proposing this systemof ternary diagrams to conclude the relative age of two inks of thesame composition that are entered on the same paper.

As a consequence the proposed method should be appliedmainly for ink entries in dairies and similar documents were morethan two inks samples may be found in chronological order.

4.5.5. 2005—Andrasko, Kunicki

In 2005, Andrasko and Kunicki [8] ran a study on ink aging inball point pen chambers, particularly near the end of theinstrument, finding that there was no indication of aging in termsof changes in the composition of dyes within a regularly used ballpoint pen, but detecting what was sometimes considerable agingin inks near the tip of the chambers not used to write for severalyears. In this case, PE evaporation was detected as well as the agingof the cationic dye mixture. This was only detected in the first threecentimeters of writing, except for a BIC ball point pen which wasobserved for the first 50 cm.

4.5.6. 2005—Siegel, Allison, Mohr, Dunn

In 2005, Siegel et al. [52] published a study on the use of LDI/MSto not only explain the structures of dyes used in ink manufactur-ing but also to follow up on the chemical variations that thesepresent over time. The dyes were artificially aged by Using UV orincandescent light and then analyzed by LD/MS to characteriza-tion.

4.5.7. 2006—Weyermann, Kirsch, Costa-Vera, Spengler

In 2006 Celine Weyermann et al. [53] did a study on agingprocesses, concretely on the loss of colour of ball point ink dyes on

paper. More specifically, the degradation processes of MV, and EV,were studied using laser desorption ionization (LDI) in comparisonwith matrix assisted laser desorption ionization (MALDI), and MassSpectrometry (MS) directly on paper. The influence of the samplepreparation technique was evaluated by comparing MALDI-MSspectra of extracted ball point strokes in the solvents. The possibleapplication of these methods to forensic document examinationwas also evaluated.

MALDI differs from LDI in the use of a matrix mixed with ananalyte before the analysis that absorbs light at a given laserwavelength, which allows the compounds, that do not absorb laserlight to be desorbed and ionized without much fragmentation.Generally, the addition of the matrix improves the sensitivity ofLDI-MS. The matrix protects the analyte and helps in the ionizationand desorption process. 2,5-Dihydroxybenzoic acid powder (DHB)was used and prepared at a concentration of 10 mg/unit in asolution of H2O:EtOH (3:2).

The degradation of ball point ink dyes was studied underlaboratory conditions influenced by different factors such as light,light wavelength, heat and humidity. Later, strokes from the sameball point pen were allowed to age naturally in the dark or underthe influence of light for a year and then analyzed.

The results showed that the degradation of dyes is directlyinfluenced by light. Humidity also increases the degradation,which can be explained by the alkaline nature of the paper (whichhas a thin calcium carbonate layer for bleaching purposes). Theinfluence of heat in the degradation process was very weak.Likewise, it was observed that the dyes did not suffer greatdegradation after a year of storage in the dark.

For the realization of this study, pure MV and Ethyl Violet, EV,(purchased to Fluka and Sigma–Aldrich companies, respectively)and also ink strokes made with a BIC medium blue ball point penwere used. Being submitted to artificial aging and natural aging(the ball point pen inks: it was written every month for a year, onetest sample was kept in the dark and the other in daylight—inwinter and summer).

The sample treatments consist on heating the samples at 100 8Cin an oven to exposure the sample to light; a Xenon light pressurelamp was used in a wavelength range 250–1000 nm with highfluence.

The sample preparation was carried out as follows:

Dissolved references substances in methanol and analyzed 0.5 mlThe ball point entries were extracted from about 2 cm strokes inethanol, TFE, phenoxyethanol and BIC mix (ethoxyethoxyehta-nol:dipropylen glycol 1:2) during 10 min at 60 8C.

MALDI/MS for pure MV and EV compounds are characterized bythe presence of the molecular ions M+ = 372.2 u and M+ = 456.3 u,respectively; it was observed that EV and MV degradation underthe influence of light was characterized by a loss of CnH2n groups.MV presents six degradation products (D = 14 u) and EV anothersix (D = 28 u), Table 5.

The degradation is quantified by the relative peak area of (RPA)

RPAi ¼Ai

Atot

� �� 100%

where Ai is the area of an ion signal for a m/z = i and Atot is the totalarea of all the signals.

Table 6Chronology of ink dating based on the degradation suffered by its dyes.

Year Author

1993 Aginsky Micro-spectrophotometry/change of color with strong organic bases.

1993 Aginsky Degradation of CV and MV, appearance of Michler’s ketone and phenol.

1995 Aginsky Micro-spectrophotometry/Dye proportion method.

2001 Lyter, McKeonwn TOF-SIMS

2001 Grim, Siegel, Allison LD/MS

2001 Andrasko HPLC/tri-dimensional diagrams CV!MV!TPR

2005 Andrasko, Kunicki HPLC

2006 Siegel, Allison, Mohr, Dunn LDI/MS

2006 Weyermann, Kirsch, Costa-Vera, Spengler LDI-MS, MALDI-MS. MV and EV Study

Fig. 7. Main pigments in gel inks.


With this definition the RPAi age curves are constructed basedon time and these fit in an exponential function as follows:

y ¼ y0 þ Aeð�x=zÞ

where X is the time, y is the RPA value, y0, A, z are constants.Among the conclusions to this study are the following:

1. The extraction of the analyte with a determined solvent caninduce undesirable effects.

2. A laser’s high density energy has as a consequence greaterfragmentation of the molecular ion. Therefore, a density ofenergy near the detection threshold of the ion has been used.

3. MALDI and LDI-MS contribute valuable information about thedegradation of inks.

4. The age curves used are a tool that gives a lot of information onthe process of degradation process of dyes, with reproducibleresults and a very small error margin.

5. The degradation of dyes depends significantly on the storageconditions of the sample.� The degradation of dyes is caused mainly by the absorption of

light with wavelengths in the UV and at the dyes’ maximumabsorption.� High humidity conditions in the presence of light increase the

degradation of dyes. (a dry environment for storage isadvisable)� Heat is a weak influence in the degradation of dyes, but can

mainly be considered especially for exposures of over 100 8C.� The strokes kept in the dark at room temperature did not show

any degradation after a year. But, it is necessary to know thestorage conditions to give an accurate interpretation throughthe evaluation of dyes of an ink for forensic purposes.

6. After developing this study, a priori condition is postulated: theinitial composition of the ink must be known for theinterpretation of a MS.

In Table 6, analytical methods of ink dating described abovebased on the dyes degradation studies are collected.

5. Gel ink dating

5.1. Composition of gel ink pens

Gel ink pens became popular writing instruments all over theword due to its smooth writing characteristics since 1984, whenthey were first manufactured.

Until now, there have been developed several methods with theaim of analyzing and classifying them. In this sense, Mazzela,Khanmy-Vital [57] examined and classified various gel inks in2003 using filtered light examination, Raman spectrometry andSEM. On the other hand, Wilson et al. [58] developed a systematicdetermination of black gels using optical and chemical techniques,i.e. microscopy, vis, NIR reflectance, NIR luminescence, TLC, spottests and GC/MS.

In 2005, Mazzela and Buzzini [59] established that among bluegel inks, based on pigments, the following two were mostlydetected: Blue 15 (C.I. 74160) Phthalocyanine blue, and Violet (23C.I. 51319) Carbazole violet (Fig. 7).

5.2. Gel ink dating

The only researches carry out about dating gel inks appeared in2006. The publications about this subject are the followings:

1. Study of the degradation of blue gel ink dyes by IP-HPLC andelectrospray sequential ionization–mass spectrometry ESI-MS/MS [55].

2. Dating black ink strokes of roller ball and gel by GC and UV–visspectrophotometry [56].

3. Classification and dating of black gel inks by Ion-Pairing High-Performance Liquid Chromatography (IP-HPLC) [54].

5.2.1. Study of the degradation of blue gel ink dyes by IP-HPLC and

electrospray sequential ionization–mass spectrometry (ESI-MS/MS)

Yi-Zi Liu et al., in 2006 published a study on the degradation ofblue gel ink dyes by IP-HPLC and electrospray sequential ionizationmass spectrometry ESI-MS/MS [54].

In the first part of this research IP-HPLC with UV detection wasused to analyze the blue gel pen inks and their photo-degradationproducts after an aging process.

Experimental procedure I: 47 blue gel pens were collected frommarkets. The aging samples were carried out exposing inksamples to UV light at 254 nm and to a fluorescent tube fromabout 10 cm distance. Naturally aging samples were sotred in


natural conditions at room temperature and preserving fromsunlight. For each sample, 5 cm ink line was cut out andextracted with 0.5 ml TBA/acetonitrile (1:1) during 10 h atroom temperature.The chromatographic conditions were optimized by selectingsuitable ion pairing reagent for achieving a satisfactory separationof dyes, its concentration and pH value. A series of volatile and nonvolatile ion pair reagents alkyl ammonium salt with differentalkyl chain were studied such us TEA, TBA, TBABr, and DHA. TBAacetate was chosen as the ion pairing reagent to perform IP-HPLCanalysis at pH 7.0. The UV detector was set at 580 nm.A previous solubility test with methanol of 47 gel inks wasperformed with the purpose of separating two groups, thoseinks based on dyes, 27, and those based on pigments, 20. Theselatter could not be extracted from the paper for a subsequentHPLC analysis; while the first 27 were separated by IP-HPLC,efficiently separating all the dyes.An ink was taken at random, G7 and its aging process followed;on the one hand under fluorescent light and on the other innatural aging conditions during 9 months.Findings. Two peaks were initially observed; peak 1 with aretention time of 6.2 min and peak 2 with a retention time of8.3 min. After putting the sample under fluorescent light it wasobserved that two new peaks appeared; 3 and 4, with retentiontimes of 3.9 and 4.9 min respectively, which indicated that newcomponents had formed.

The two new peaks become more prominent with the age;whereas, weaker peaks appear around these after 36 h underfluorescent light. After 100 h these small peaks become moreprominent while the intensity of peak 1 decreases with time.

For inks recorded in natural conditions two main peaks wereobserved (that concur with the aforementioned with retentiontime of 6.2 min and 8.3 min), but there was practically no change inthese peaks after 9 months of storage with the exception that therelative intensity of peak 1 slowly decreases, while peak 2 slowlyincreases. This phenomenon illustrates that the component of peak1 decomposes in natural aging conditions. These results are not thesame ones than those shown by Andrasko [8,50,51].

In the second part UPLC/MS/MS is used to identify the dye andits degradation products. Ammonium Carbonate was used as ionpairing reagent because TBA produced interferences. It wasinferred that the molecular ion of molecular weight 749 was‘‘Acid Blue 9’’ (brilliant blue FCF, food blue 2, etc.) (Fig. 8)

Several degradation processes of this dye and also severaldegradation compounds of this main dye are proposed.

5.2.2. Dating black ink strokes of roller ball and gel by GC and UV–vis

spectrophotometry [56]

This study on the dating of water-based inks (so much the rolleras gel) was presented by Yuanyan Xu, Jinghan Wang, Licuan Yaowho used GC and UV–vis spectrometry [56].

Fig. 8. Acid Blue 9 Structure.

In this study, 6 German and Japanese roller and gel inks areanalyzed. Their storage conditions are a drawer. Two centimeterssamples are taken and analyzed with GC and UV-vis. Each sampleis extracted and then placed into a vial with 1 ml of methanol thatcontains ethyl benzoate during 20 min. After which 2 ml of eachsample were analyzed with GC. The residual solution wasextracted with 0.9 ml of FMF during 20 min to maximize the totalamount of dye. Then UV–vis spectra were registered. For eachsample, absorption measurements for the maximum absorption ofthe dye present in the ink are read. This absorption is taken intoaccount with the purpose of eliminating the influence of thethickness of the ink in the stroke.

The aging parameter is defined as follows:

Ratio ¼ ApeakðsolventÞ=Apeakðexternal comparative matterÞ� �� Apeak ink

The aging curve is established, drawing the ratios versus the age ona graph. Through these curves, the age of a questioned documentcan be calculated. If the ink samples have two or more solvents,two or more age curves will be obtained.

In order assess the absolute age of the ink, that is to say, in orderto make an evaluation of the ink without the necessity of an inkreference for comparison other percentage D are established, andthe D values related to age are established.

The ink strokes are heated up to 60 8C in an oven for 1 h, and D isdefined as:

D% ¼ ½ðR� RTÞ=R� � 100%

where R is the value of the ink ratio without heating and RT is thevalue of the ratio of the heated ink.

Depending on the D values, ink ages can be established on thefollowing way:

30% � D% < 80% the inks are fresh.0% < D% < 30% the inks are between 10 and 90 days.D% = 0 the ink is old having over 90 days.

In no case, throughout the whole article, is reference made tothe solvent(s) being analyzed.

5.2.3. Classification and dating of black gel inks by Ion-Pairing High-

Performance Liquid Chromatography (IP-HPLC)

This study is made on the basis of tracking on the colorants of asample set of 93 black gel ink instruments. Running a previoussolubility study with methanol, they are divided in two groups:those that have an ink based on dyes, a total of 50, and those thathave an ink based on pigments, a total of 43 (this does not meanthat inks based on dyes do not contain some pigment).

The dye based gel ink group is normally acid dyes or direct dyesthat are ionic compounds and more easily extracted from the paperthan pigments. In this study, IP-HPLC with UV detection at 580 nm,which is a powerful method to separate ionic compounds, is usedto analyze ionic dyes of gel inks, assuming that the study of dyesgives more useful information to assess the age of the ink than thestudy of pigments.

Experimental procedure: Five centimeters ink line was cut outfrom the paper and the ink entries were extracted by addition of0.5 ml TBABr 40 mM:acetonitrile (1:1) for 12 h at roomtemperature. A series of solvents and mixtures of solventswith different polarities was examined to extract the dyes. Amixture of a buffer solution at pH 7.0 of TBABr and acetonitrile1:1 as eluent was employed.Findings: It was discovered that all inks have 2 or more dyes, andthey were again divided in three groups depending on theretention times and the number of dyes present.


Fifty percent (50%) of analyzed inks belonged to the first of thegroups which displayed peaks at 8.8 min; 10.8 min; 13.1 min;20% of analyzed inks belonged to a second group thatdisplayed peaks at 6.2, 8.8, 10.8, 13.1 min; and 16% of theinks composed a third group that displayed peaks at 7.0,15.3 min. There are a percentage of inks, which could beincluded in a fourth group that has more than twochromatographic peaks but whose retention times aredifferent between themselves. Within each group the differentink formulas present the same dyes but with differentpercentages of each (which is translated in the areas of thepeaks). At no point throughout the study is mention madeabout any of the peaks having been identified.The aging for each of the groups has been tracked separately bytaking, at random, one ink from each group (no. 32 for the firstgroup, no. 1 for the second group, and 21 for the third group).Group 1: Peaks 1 and 2 decrease with time whereas group 3increases gradually, not originating new peaks in the chroma-tograms, and so much the samples aged with ultraviolet light asthose that underwent natural aging.Group 2: The dyes of this group decompose easily. Peaks 5 and 6are more prominent after storing for four weeks in environ-mental conditions, peak 4 obviously decreases. It is deducedthat compounds 5 and 6 are originated by degradation ofcomponent 4 based on the fact that no new peaks appear afterthe degradation of peaks 1 and 3. On the contrary, the weight ofpeaks 5 and 6 decreases with increasing age under UV light. Therelative changes in the weight of the peaks reflect thedecomposition speed of dyes and the increase of the relativeweight of the peaks indicates that the decomposition speed ofthe relevant components is lower than those of othercompounds.When the aging has been achieved naturally it is observed thatthe changes in the composition were significant with time.Peaks 5 and 6 that have been discussed above, and thatappeared after a week of storage, disappeared after 13 monthsin natural aging conditions. The tendencies of the changes in thecomposition were slightly different from the samples agedunder light. The relative weight of Peak 3 increases with time innatural aging, and indicates that the decomposition speed ofthis component is smaller than any of the other components inrelation to its degradation in artificial aging by light.Component 4 decomposes very quickly the first days whereasthe speed of decomposition decreases later. Component 4 canbe more sensible to air, with the most superficial layersdecomposing and the deepest layers presenting little influence.Peaks 2 and 3 are the same as the previous group and theirchanges with time can contribute information on the age of theink. The changes in the relative weights of peaks 4, 5 and 6 cancontribute the key to differentiate inks from the second group ofthose of the first.Group 3: Ink 21 was selected as representative of the group. Thechromatogram displayed two main peaks; 1 and 2 and twoother smaller peaks, 3 and 4. With time in the samples exposedto fluorescent light, peaks 1 and 2 decrease, whereas 3 and 4increase. The results are not consistent with those of thesamples aged with UV light.For inks aged under natural conditions, in addition to theaforementioned four peaks, appear peaks 5 and 6 close to peak 4and 1, respectively. Peaks 3 and 4 behave as those samplesexposed to fluorescent light, increasing, whereas peaks 1 and 2decrease with time. Peaks 5 and 6 become more prominent withtime. This fact indicates that peaks 5 and 6 are products of thedegradation of peaks 1 and 2.The mechanisms of aging of these inks based on the degradationof dyes have been studied. This degradation is reflected in the

chromatograms, establishing differences in the aging mechan-isms when it has been performed naturally or artificially.

6. Conclusion

The present revision includes major articles and/or contribu-tions to conferences since the year 1920 through 2008 in the fieldof the ink dating. From them, we can deduce that ink dating is anextremely complex problem, due to the amount of variables thatinfluence the ink–paper system, and despite the valuablecontributions that have been achieved in this field, no solutionhas yet been found.

Prior to 1950, separation techniques were foreign to the field ofink analysis because the methods themselves were in fledglingstages of development. Document examiners relied upon filterphotography, alternate light sources, and chemical spot tests todifferentiate ink samples. Non destructive methods such as IR anddiffuse reflectance IR, microspectrophotometry, visible and IRLremain important, valuable tools for the document examiner. Infact, TLC is one of the most popular methods because its use and itsability to quickly generate qualitative information unavailablethrough non-destructive spectroscopy. TLC it is not the mostindicative technique neither to study non coloured components ofinks nor to make quantifications; so, much research has beendeveloped to explore other applications of instrumental techni-ques, especially GC, for the analysis of VCs in ink dating procedures.

From the point of view of analytical chemistry, accuracy andrepetitivity play an important role. Accuracy of the agingtechniques due to aging curve is a decreasing exponential curveand therefore, accuracy decreases dramatically as the agingprocess levels off. And repetitivity measurements must beconducted when determining relative age of ink to show howreproducible or reliable the measurement is.

It is now widely accepted that the dating methods based onartificial aging and sequential extraction of dyes are not reliable[1,60–63].

Nowadays the main method used by a variety of laboratories inUSA and in Europe to date inks is comparing an ink to itself,exposing it to artificial aging and comparing the concentration ofvolatile compounds of the aged ink with those from that same inkwithout aging, concretely, phenoxyethanol for ball point inks.

PE has been the most studied compound using the mostsophisticated instrumental techniques, mainly:

- Thermal desorption and SPME for the separation step;- GC/FID or GC/MS for the identification and quantification.

This method has its limitations, however, due to:

1. Volatile compounds stabilize after a period of approximately 2years; if the ink is older it cannot be concluded.

2. PE, can migrate through the paper and from one sheet of paperto another when they are stored successively.

3. The latest research carried out at our laboratories [64]. allow usto spot several error sources in the methods mentioned abovewhich are still unstudied such as the different kinetics in the lossof PE, mass invariance, importance of the extraction times, crosscontamination, etc. These error sources can lead to mistakenconclusions in many cases. In our experience those methods aresuitable only in a very few number of cases.

It is important to emphasize that most investigations arecentered on the ink of the glycol based ball point pen, and that theonly studies known for non-ball point inks are those elaborated forgel inks.


About gel ink dating poor knowledge has been carried out. Thecompositional changes of different classes of gel inks studied havea tight relationship with the aging of time, although themechanism of their compositional changes were complicatedand not understood yet. Nevertheless, some difference has beenobserved in the aging process of the gel ink entries on paperdepending on conditions, which are useful to identify whether asuspicious document was artificially treated or not.

A third way is the study of the polymerization of resins. Thereare very few number of research in this field, the most importantand recent are the ones done by Kirsch [30–32]. However, this is anunexplored way which could give satisfactory results unless itsresearch is very complex.

It is expected that the use of non-destructive, greater sensitivityand resolving power techniques will further improve the chemists’ability to resolve the studies in the forensic ink dating field.

Final recommendations for future works can be summarized asfollowing:

1. Need for inter-laboratory validations of the methods based onthe loss of volatile components. According to our latest studiesthe Retention Time Lock mode in GC–MS [64] can be used as areally useful tool for the inter-laboratory validations.

2. The further study of the kinetics of the resins with time and itsuse in ink dating.

New investigations about resins are more promising for agedetermination over a longer time range.

Acknowledgements

We really much appreciate the invaluable collaboration givenby Ph. D. Anthony Cantu in the revision of the full article, and alsofor his really interesting suggestions. Authors also thank theUniversity of Basque Country/EHU for financial support. Finally, wealso thank very much Ms Ruth Wolff for her final English revision.

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