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Research ArticleReceived: 25 October 2009 Revised: 28 February 2010 Accepted: 1 March 2010 Published online in Wiley Interscience: 7 May 2010

(www.interscience.com) DOI 10.1002/xrs.1257

SANDRA: a portable XRF system for the studyof Mexican cultural heritage†

J. L. Ruvalcaba Sil,∗ D. Ramírez Miranda, V. Aguilar Melo and F. Picazo

This work presents the portable X-ray system SANDRA (Sistema de Analisis No Destructivo por RAyos X or System for NonDestructive Analysis using X-rays) developed at the Physics Institute of the UNAM, Mexico, for the study of Mexican culturalheritage collections. The X-ray fluorescence (XRF) SANDRA device can use 75 W Mo, Rh and W X-ray tubes and Amptek Si-PINand Cd-Te detectors that are selected and combined depending on the elemental range detection requirements and the specificproblem to be studied. In this paper, a full description and characterization of this system, sensitivities for the X-ray tubes anddetectors as well as the detection limits are discussed. Examples of applications to technological studies on pre-Columbianmetallic artifacts and analysis of color materials of ancient Mexican codex are shown. Copyright c© 2010 John Wiley & Sons, Ltd.

Introduction

X-ray fluorescence (XRF) is a fast and high sensitivity multielemen-tal technique; it can be applied directly for non-destructive andnon-invasive studies.[1,2] This technique is well established as a ba-sic analytical tool for cultural heritage applications for more than30 years.[3 – 13] Although there are many museums and conserva-tion laboratories equipped with static or portable XRF equipmentsin developed countries, nowadays, the use of portable devicesfor the characterization of objects and collections of museums,libraries, or in general, materials from the archaeological record orart history is fortunately increasing in countries of Latin America.

Since the early works using portable XRF systems[1,3,5,7,11],many improvements have been achieved.[1,2,14 – 16] With thedevelopment of Si-PIN and silicon drift detectors,[17 – 19] thesystems became lighter and the portability was significantlyimproved for in situ measurements. Thus, several systems havebeen developed in many countries, mainly in Europe. Currently,different types of X-ray sources – including radioactive sourcesand X-ray tubes – and detectors are used.[20 – 25] XRF apparatusare extensively applied for the characterization of all kindof cultural heritage’s materials.[26 – 33] Often, XRF analyses arecomplemented by other portable spectrometers, such as theRaman ones,[13 – 34] and also using other X-ray based techniquessuch as particle induced X-ray emission spectroscopy (PIXE).[35,36]

The last improvements on XRF systems consider the developmentof devices combining X-ray diffraction (XRD) and XRF in situ.[37 – 39]

Despite the rich cultural heritage of the Latin American areaand the improvements in the experimental devices, very fewportable XRF equipments have been developed in the last yearsin this region.[40 – 42] This paper presents the portable X-ray systemSANDRA (Sistema de Analisis No Destructivo por RAyos X or Systemfor Non Destructive Analysis using X-rays) developed at the PhysicsInstitute of the UNAM, Mexico, for the study of outstandingMexican cultural heritage collections. The main applications ofthe SANDRA system are related to pre-Columbian and colonialmanuscript analyses, paintings for palettes studies and painter’stechniques from colonial to modern periods, 16th–17th centuriespolychrome colonial sculpture, pre-Columbian metallic artifacts(gold, bronzes), pre-Hispanic turquoises and green stone objects,

as well as ancient photographs. Some examples of applicationsare also discussed in this paper.

The SANDRA System

Our actual SANDRA system is the result of a previous prototypewith a Rover system with Si-PIN and CZT X-ray detectors fromAmptek.[41,42] In the past years, it has been renovated andnew detectors may be used. To improve our system, severalcomparisons with PIXE and RBS measurements have been carriedout on book’s decorations from 17th to 19th centuries,[43] Mayapottery and pre-Hispanic copper artifacts.[44]

SANDRA system has a typical geometric configuration; thedetector is set at 45◦ from the direction of the excitation X-rays(Fig. 1). The available X-ray tubes have Mo, Rh and W anodes with125 µm beryllium window. The maximum power of the X-ray tubesis 75 W (50 kV, 1.5 mA). They correspond to the XTF5011 modelfrom Oxford Instruments. The X-ray tube is powered by a highvoltage power supply XLG50P100 from Spellman. The X-ray tubeis mounted on an X–Y–Z support, so it can be manually moved3 cm in each direction in front of the studied object to smoothlyreach the selected region of analysis. Three small fans and a mainfan at the bottom of the X-ray tube provide the necessary coolingfor the X-ray tube. A thermocouple is provided in the X-ray tubefor temperature monitoring. The maximum X-ray tube operationtemperature is 50 ◦C.

The SANDRA system is mounted on an articulating arm boomstand that ensures high mobility and flexibility in the movement(Fig. 2). With this setup, it is possible to reach corners and difficultlocations on the studied object. The system can be used for analysison the vertical and horizontal planes or it can be tilted as necessary.

∗ Correspondence to: J. L. Ruvalcaba Sil, Instituto de Física, Universidad NacionalAutonoma de Mexico (UNAM), Apdo. Postal 20-364, Mexico DF 01000, Mexico.E-mail: sil@fisica.unam.mx

Instituto de Física, Universidad Nacional Autonoma de Mexico (UNAM), Apdo.Postal 20-364, Mexico DF 01000, Mexico

† Article published as part of the special issue on Portable X-ray Spectrometers.

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SANDRA portable XRF system

focusable lasers

region ofanalysis

webcamSi-PIN detector

X-ray tube X-Y-Zsupport

beamshutter

fans

Figure 1. The SANDRA XRF system during the study of a collection ofMexican historic photography. Main components are pointed out.

Figure 2. The SANDRA XRF system supported on its articulating arm boomstand. Analysis of the Colombino codice.

The X-ray beam diameter is determined by a lead collimator.The beam diameters may be 0.5, 1.0, 1.5 and 2.0 mm. Two X-raydetectors can be used: a Si-PIN detector (XR-100-CR model) anda Cd-Te detector (XR-100T-Cd-Te model) from Amptek. The Si-PINdetector has a 6 mm2 active area, a 500 µm thickness and a 0.5 µmBe window while the Cd-Te detector dimensions are 5 × 5 × 1 mm(25 mm2 active area) and 4 µm Be window. The energy resolutionat 5.9 keV (Mn-Kα line) of the Si-PIN and Cd-Te detectors are 180and 360 eV, respectively. A conic piece in aluminum covers thedetector head for its protection and it could be used to set aHe jet for light elements detection improvement. The cone has acylindrical aperture of 4 mm of diameter. Under this configuration,this cone is working as a collimator only for the Cd-Te detector,as the exposed area is then 12.5 mm2, a half of the total detectoractive area.

The X-ray detector signal is processed by a PX4 digital pulseprocessor from Amptek before reaching the laptop computer.Recently, the complete X123 Si-PIN spectrometer system fromAmptek has been tested as well. This system provides togetherthe X-ray detector, the amplifier and the power supply in a smallpacking and it is directly connected to the computer by a USB

cable. The performance of this Si-PIN detector is similar to the onedescribed above.

For the SANDRA operation a LED security light turns on whenX-ray tube is working. The X-rays from the tube can be stopped bya shutter. To determine the region of analysis, two focusable laserpointers intercept at 8 mm from the X-ray tube exit collimator. AnX-ray screen may be used to set properly the working distanceand the laser pointers. The total distance from the X-ray tube exitwindow to the sample surface is 9 cm while the X-rays emittedfrom the sample have to travel 1.5 cm in air before reaching thedetector. The incident X-ray beam spot at the sample surface wasmeasured for 1.0, 1.5 and 2 mm diameter using 250 µm diameterAu wire and mounted on a XY translation stage with 10-µmresolution. We determined that there is no significant scatteringand the increase in the beam diameter is lower to 15% of thecollimator diameter.

Considering the previous parameters, Rh and Mo K peaks fromthe X-ray tube loss only 1% of their intensities in the air pathwhile L lines from Mo and Rh have a significant absorption andonly 3.6 and 12.6% may reach the sample, respectively. For thisreason, the corresponding X-ray scattering is very weak and it isnot often detected. The Mo-L peak may overlap S-K and Pb-Mpeaks, whereas the Cl-K peak may be overlapped by Rh-L peak.On the contrary, W Lα and Lβ lines show a lower absorption in air(about 10%), then the scattering peaks are frequently observed inthe spectra using the W X-ray tube. Nevertheless, the Mo, Rh andW L peaks may be easily removed using filters in the incident X-raypath, such as a foil of 12 µm of Cr or Zn.

On the other hand, only the X-rays emitted from sample by thelighter elements are absorbed significantly in the 1.5 cm air path.For Al, Si, S, Cl, K, Ca, Ti, Fe and Cu Kα the transmitted X-rays are 5,24, 36, 51, 61, 76, 85, 92, 97 and 99%, respectively. This fact meansthat if low energy X-rays detection is required for the analysis withour equipment, it will be necessary to use a He jet at the X-raydetector and at the path of the X-ray incident beam as well.

Finally, to improve the data record during the analysisand to observe the irradiated region at the object surfacesimultaneously to the X-ray spectra acquisitions, a webcam withmedium resolution is used. In this way, both an image and thecorresponding spectra are stored in the computer.

Characterization of the XRF System

The full characterization of the SANDRA system was required todetermine their advantages and limitations, as well as the mostsuitable configurations.

Measurements on a full set of standard reference materials fromMicromatter Co. were carried out for the Mo, Rh and W X-ray tubesand the Si-PIN and Cd-Te detectors. The elemental range coveredfrom Si to Sn for K and L lines and Pb and Au L lines. From the X-rayfluorescence spectra, the sensitivity was calculated[1] from the ratioof the peak area (counts) and the product of the concentration(µg/cm2) and the time (s). For calculation of sensitivities, peakareas were measured using AXIL program.

Figures 3 and 4 show the sensitivity curves as a function of theX-ray energy for the Si-PIN and the Cd-Te for the Mo, Rh and Wunder the same voltage and current conditions (45 kV and 0.3 mA).Filters were not used.

From the sensitivity curves, it is clear that the W X-ray tube givesrise to higher sensitivities for both detectors from 3 to 8 keV (K toCu) mainly due to the W–L lines excitation while for the higher

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J. L. Ruvalcaba Sil et al.

Sen

sitiv

ity (

coun

ts/ µ

g/cm

2 * s

)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 3010-3

10-2

10-1

100

MoRhW

X-ray energy (keV)

Si

Ca

V

FeZn

Br

Sr

Ag

SnAs

Si-Pin detector

Cl

Figure 3. Sensitivity curves as a function of the X-ray energy using theSi-PIN detector and the Mo, Rh and W X-ray tubes under similar conditions(0.3 mA, 45 kV). A set of Micromatter Co. thin reference materials was used.

MoRhW

Cl

Ca

V

FeZn Br

Sr

Ag

Sn

As

Cd-Te detector

Sen

sitiv

ity (

coun

ts/ µ

g/cm

2 * s

)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 3010-2

10-1

100

101

X-ray energy (keV)

Figure 4. Sensitivity curves as a function of the X-ray energy using theCd-Te detector and the Mo, Rh and W X-ray tubes under similar conditions(0.3 mA, 45 kV). A set of Micromatter Co. thin reference materials was used.

energy range (10–26 keV) the sensitivies are similar by comparisonto the Mo and Rh X-ray tubes.

On the other hand, despite a rapid decrease in the sensitivityfor the Si-PIN detector and the Rh tube for X-ray energies higherthan 18 keV, the sensitivies are very similar for the Mo and Rh X-raytubes from Si to Sr. For energies lower than 14 keV, the Mo-K linesare energetically closer to the K-edge of the elements in this rangethan the Rh-K lines (and therefore the respective photoelectriccross sections are higher). However, the Rh anode source offersmore intense bremsstrahlung radiation in the same range which isactually the most significant contribution in the ionization processof the corresponding elements. For these reasons the sensitivitiesare comparable.

A comparison between the sensitivities normalized by Fesensitivity for the Si-PIN and the Cd-Te detectors using the MoX-ray tube is shown in Fig. 5. It is observed that the normalizedsensitivities for the Si-PIN detector are higher in the light elementsrange (the factor decreases from 3 for Cl when the X-ray energy

Si-Pin K linesSi-Pin L linesCd-Te K linesCd-Te L lines

Mo X-ray tube

Si

Ca

V

Fe

ZnBr

Sr

Ag

Sn

Pb

Cl

Au

Sen

sitiv

ity n

orm

aliz

ed b

y F

e se

nsiti

vity

10-3

10-2

10-1

100

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

X-ray energy (keV)

Figure 5. Comparison between the sensitivities normalized by Fe sensitiv-ity for the Si-PIN and Cd-Te detectors for the Mo X-ray tube under the samepower conditions (0.3 mA, 45 kV).

Mo X-ray tube

Si-PinCd-Te

Si

CaTi

Fe Zn BrSr

Ag

Sn

Cl

Det

ectio

n lim

it (µ

g/cm

2 )

10-1

100

101

10 15 20 25 30 35 40 45 50 55

Atomic number Z

Figure 6. Detection limits comparison for the Si-PIN and Cd-Te detectorsfor the Mo X-ray tube under the same excitation conditions (0.3 mA, 45 kV).A set of Micromatter Co. thin reference materials was used.

increases). In the medium X-ray energy range (from V to As),the normalized sensitivities are very similar and they are slightlyhigher for the Cd-Te detector from 11 keV. Nevertheless, for X-rayenergies higher than 18 keV the normalized sensitivities for Cd-Teare higher than the Si-PIN normalized sensitivities from a factorof 3.5 up to 7 as X-ray energy increases. The Cd-Te detectionstarts from Cl because of the low energy X-ray absorption in itsthick window (4 µm), but the Cd-Te efficiency increases rapidly forhigher energies improving its sensitivity.

The detection limits[2] calculated as the ratio between theproduct of the concentration by three times the square root ofthe background and the peak area, for the Mo X-ray tube and forboth detectors, show that the lower detection limits are reachedin all the cases for the Si-PIN detector (Fig. 6). Peak to backgroundratios are in general higher for the Si-PIN detector than for theCd-Te detector. For Fe, these ratios are 0.97 and 0.7 for the Si-PINand the Cd-Te detector, respectively, while for Ag the same ratiosare 0.92 and 0.57. Despite the higher sensitivity for the Cd-Te in

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SANDRA portable XRF system

Sediment (SRM 2711, 2704)Tomato leaves (SRM 1573a)Gold alloy (588/340)

Ca

Si

Fe

CuAu

Ag

Pb

BrSr

Cl

Mo X-ray tubeSi-pin detector

Det

ectio

n lim

it (µ

g/g)

102

101

103

104

0 42 86 1210 14 16 18 20 2422 26

X-ray energy (keV)

Figure 7. Detection limits for the Si-PIN and Cd-Te detectors for the MoX-ray tube (0.3 mA, 45 kV) from solid reference materials NIST SRM 2704,2711, 1573a and a Degussa gold alloy (Au 585/Ag 340).

the high energy range, the background in the spectrum is muchhigher and the corresponding detection limits are larger.

On the other hand, several reference standard materialsfrom NIST were used to evaluate the detection limits for solidsamples analysis: SRM 2704 Buffalo river sediment, SRM 2711Montana sediment unpurified, SRM 1573a Tomato leaves anda homogeneous gold alloy reference 585/340 from Degussawere irradiated by 5 min using the Mo X-ray tube and the Si-PIN detector. The X-ray tube power parameters are 45 kV and0.3 mA. Considering the same detection limit criteria as above,the graph shown in Fig. 7 was obtained. For sediments and theplant reference, the detection limits may reach 40 µg/g for Cu and25 µg/g for other heavier elements, like Sr. Detection limit for Feincreases to 100 µg/g while for Ca and Cl, the detection limits are400 and 1000 µg/g, respectively. We may expect similar results forother materials with a matrix similar to sediments (stone, glass).For the gold matrix, Cu has a detection limit of 450 µg/g and Agmay reach 2400 µg/g while the Au may attain 1340 µg/g.

From the previous measurements, we can conclude that aMo or Rh X-ray tube with a Si-PIN detector represent the bestcombination for a first general analysis including light elements.Cd-Te detector may be useful for the detection of higher X-rayenergies or heavier elements. The combined use of these X-raydetectors may also be considered.

Some Applications to Cultural Heritage Studies

For research in cultural heritage and a first characterization of acollection or specific objects, XRF in situ is a powerful analyticaltool. XRF analysis provides enough information in short time toestablish the nature of the materials (inorganic or organic) andthe use of complementary techniques. After a collection studyby XRF, it is possible to select representative objects for furtherstudies in the laboratory or, if necessary, to determine a strategyof sampling with minimum damage to the objects. This analyticalapproach has been adopted for the study of Mexican collectionsby our interdisciplinary group. After the application of imagingtechniques and microscopical examination, XRF is applied and

complemented by Raman spectroscopy, Mid-Fourier-transforminfrared (FTIR) in situ and VIS-NIR light spectrometry.

Our SANDRA system has been extensively used for the study ofMexican cultural heritage collections since the construction of ourfirst prototype several years ago. Due to the success of this device,other apparatus have been constructed. Actually, three devicesare operational and they are used in collaboration with the mostrelevant Mexican museums. The main applications are related tostudies of pre-Columbian and Colonial manuscripts, paintings forpalette and painter’s techniques from Colonial to modern painting,polychrome colonial sculptures, pre-Columbian metallic artifacts(gold, bronzes), pre-Hispanic turquoises and green stone pieces, aswell as historic photographs. Recent applications include metallicthreads and textiles. In this work, two examples of our researchesusing the SANDRA system are presented.

Pre-Columbian gold and silver artifacts

In Mexico, few pre-Columbian artifacts and collections of preciousmetals are preserved. Most important items are kept in nationalmuseums and due to their importance it is very difficult to transportthem to laboratories for analytical studies, and sampling is notallowed or it is very limited. In some cases, non-destructive andnon-invasive studies were carried out by PIXE on a reduced amountof gold items[45] and previously only few artifacts were irradiatedin situ using portable XRF.[46] For this reason, scarce information onMesoamerican gold work exists and there were insufficient dataconcerning the silver artifacts before our research.

Certainly, the richest and most important collection with anarchaeological context from Mesoamerica is the Tomb 7 fromMonte Alban, central Oaxaca in the South of Mexico, correspondingto the Mixtec Culture of the late postclassic period (1200–1521A.D.). In the case of this collection, few electron microscopeanalyses (SEM-EDS) were carried out on a small number of samplesfrom selected items.[47] Recently, a set of portable equipmentswere transported to the Museo de las Culturas de Oaxacain Oaxaca City to perform a non-destructive and non-invasivecharacterization. The state of conservation of the collection is verygood. Then, for the gold artifacts and most of the silver itemsthere were unexpected important patina effects on the analyticalresults.

Considering the sensitivity data, the Cd-Te detector and theMo X-ray tube combination was chosen for this study as themetallic alloys are composed by medium and heavy elements.In particular, the detection of Ag K lines is important for thisstudy as they provide more representative information of thebulk composition than Ag-L lines. In this way, more than 600XRF analyses were performed on 49 artifacts within 5 days in themuseum during the usual opening hours. X-ray tube conditionswere 45 kV and 0.15 mA using a 1.5 mm beam spot. A spectrumrequired 60 s per region of analysis. The number of measurementson each object varied depending on the complexity of the artifactand its heterogeneity. Most complex artifacts such as necklacesrequired many analyses, and then the X-ray tube filament currentwas increased to 0.3 mA to reduce the acquisition time to 30 s andto obtain suitable spectra.

A Degussa gold alloys set (including the Au/Ag contents585/340, 750/120, 750/40, 585/140 and 900/40) as well assilver alloys (0.925, 0.720 sterling Ag) were irradiated under thesame conditions to get a suitable system calibration.[48] AXILprogram was used for X-ray peak area calculations. The elementalconcentrations were obtained following a procedure described byKarydas.[26]

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208

207

209

210211

215

212213211

Figure 8. Gold pendant of Xochipilli god, piece A. Other four similar piecescomplete the original set. Mixtec culture, Oaxaca, Mexico. ca 15th century.

Two of the artifacts, including the regions of analysis, are shownin Figs 8 and 9: a gold pedant and a silver finger ornament. Thecorresponding results are plotted in the graphs of Figs 10 and 11,respectively. The high homogeneity of the alloys composition isnot surprising.[45,49] These artifacts were casted by false filigreelost wax procedure.

For the gold pendant, the X-ray incident angle was modifieduntil a grazing geometry of irradiation in flat areas was achieved;nevertheless, gold enrichment at the surface of the gold pendantwas not observed.[50] The mean composition of this artifact isAu 46.9%, Ag 32.8%, Cu 20.3%, similar to other three identicalpendants of the collection. They may be produced in the sameworkshop with the same gold alloy. Their composition is quitedifferent if we compare it with other pieces of the collection (meanAu 77%, Ag 15%, Cu 8%).

Concerning the silver ring elemental composition, this is similarto the rest of the silver items of the collection, with Cu averagecontents of 2% and very low amounts of Au. The same alloy wasused for all the parts of the finger ornament, except for one ofthe bells (region 356), attached by a plastic wire. We can assertthat after the discovery of the tomb, this bell was added to theornament but this modification to complete the artifact is not right,as it does not match the expected composition of the artifact.

These are just few results[49]; a detailed paper with the full setof artifacts and data of the collection is in progress.

Studies of early colonial codices

In the pre-Hispanic and early colonial codices an important amountof knowledge is preserved including religion and traditions ofthe ancient Mexican people. Most of these manuscripts weredestroyed during the catholic evangelization in the 16th and17th centuries. Some of these documents survived, and nowadaysthey are kept in European collections. In the Mexican collections,only one pre-Hispanic codice, the Colombino, is preserved in the

356

348

351

350

350

352

353

354

355

357

358

359

360

Figure 9. Silver finger ornament of eagle. Other three similar piecescomplete the original set. Mixtec culture, Oaxaca, Mexico. ca 15th century.

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

10

15

20

25

30

35

40

45

50

55

60

65

Con

cent

ratio

n (%

)

Cu Ag Au

Figure 10. Elemental contents of Cu, Ag and Au determined by XRF forthe Xochipilli god pendant, piece A.

Biblioteca Nacional de Antropologia e Historia (INAH) with aboutother 40 colonial codices written after the Spanish conquest.

A research project on this kind of manuscripts has beendeveloped to determine the materials used in these documents,to understand how they were written and to propose preventiveconservation strategies. In fact, there are scarce analyses on codicematerials.[42,51]

The SANDRA system and other portable equipments weretransported to the security areas of the library to carry out theanalysis of the most important codices of the Mexican collection. In

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SANDRA portable XRF system

348349

350351

352353

354355

356357

358359

360

0.1

1

10

80

85

90

95

100

CuAgAu

Con

cent

ratio

n (%

)

Figure 11. Elemental contents of Cu, Ag and Au determined by XRF forthe silver finger ornament of eagle.

the first stage of research, the Colombino codice and two colonialcodices (de la Cruz Badiano, Azoyu) were studied.[51] In this case,we discuss the analysis of one colonial codice.

Among the most important early colonial manuscripts, the de laCruz Badiano codice was written in 1552 in the Franciscan’s schoolfor noble Indians (Santa Cruz de Tlatelolco) in Mexico City just31 years after the conquest of the Aztec capital, Tenochtitlan. ThisEuropean book style codice was discovered in the Vatican Libraryand it was given as a present to Mexico by the Pope in 1990.The main subject of this document is the pre-Hispanic traditionsof use of plants and minerals for medical purposes.[36] Themanuscript, written with iron-gallic inks within minium margins

(confirmed by our XRF analysis[52]), has colored drawings of localplants, with their names written in red ink in ancient Mexicanlanguage – Nahuatl – and the description of the recipes written inLatin (Fig. 12). Special attention was focused on the color materials.The first XRF analyses were carried out using the Cd-Te detectorand the Mo X-ray tube (45 kV and 0.3 mA using 1-mm beam spot)as mineral pigments could be found. After a first general analysis ofseveral pages at the beginning, middle and end of the document,only arsenic in one kind of yellow color, probably due to orpiment,and high iron contents (earth pigments) in brown color weredetected. Then, green, blue, red and other kinds of yellow colormay be organic as their spectra are similar to the paper one.[52]

A second round of analysis and new measurements were carriedout using the Si-PIN detector and similar X-ray tube conditions. Asan example, Fig. 12 shows the pages 9 and 12 recto of the de alCruz Badiano codex with the analyzed regions. The main resultsare plotted in the graph of Fig. 13.

The identification of two yellow was confirmed, one organicand the other one (B191) fitting the orpiment composition (As,S). The white color (B137, B195) is related to Ca and S signals, i.e.gypsum. Brown and ochre are clearly correlated to high amountsof Fe, and in some cases Mn, typical of earth pigments (B139,B194). Sometimes they can be mixed with orpiment. Despitethe variability observed for the green, blue and red colors,mainly due to the overlapping of the color layers and colorcombinations with gypsum and orpiment, the intensities of themain detected elements for these colors are very similar to thepaper signals. Considering the previous data collected with theCd-Te detector, we conclude that these colors must be organic(dyes) and the presence of Si, K and Ca indicate that clays couldbe used to fix the dye, such as in the Maya blue manufacture withindigo and palisgorskite.[53] This preparation of colors is relatedto pre-Hispanic origin and it does not correspond to European

131

132

133

134

135

136

137

138

139

140

141

142

143

188

189190

191

192

193

194

195

196 197

198

199

Figure 12. Nine and 12 recto pages of the de la Cruz Badiano codice (1552). XRF analyzed regions are shown.

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BD131

BD136

BD138

BD140

BD137

BD14

2

BD139

BD191

BD189

BD190

BD192

BD193

BD194

BD195

101

102

103

104X

-ray

inte

nsi

ty (

cou

nts

)

SiSKCaFeAsPb

green

paper

blue

whitefolio 9r folio 12rbrown

yellow

red green

brown white

Figure 13. X-ray intensities from the XRF spectra of the analyzed regions of Fig. 12, de la Cruz Badiano codice.

lacquers.[54] It is clear that the use of dyes and pigments forcoloring followed a specific pattern, like in the case of the redcolor; minium (lead tetraoxide) never appears in the figures and itwas exclusively used in the red margins and mixed in the red inksprobably with a red dye.

The de la Cruz Badiano codice shows the syncretism of the pre-Columbian and European traditions of writing at the beginning ofthe colonial period in Mexico. The European document format andbook style, written with iron-gallic inks, integrates representationsof plants with pre-Hispanic iconographical elements and a selec-tive use of dyes and pigments following the pre-Columbian codicetraditions. Only in the late colonial codices, dyes are replacedby European pigments.[42,51] Further analyses on the codices col-lection using XRF and other complementary techniques, such asRaman and Mid-FTIR in situ are in progress.

Conclusions

This paper showed the main analytical features of the portableXRF spectrometer SANDRA, developed in the Instituto the Fisica,UNAM, Mexico. It has been used for various applications includingtechnical studies of metallic artifacts (gold, bronzes), analyses ofpre-Columbian and colonial manuscripts, studies of painting forpalette and painter’s techniques, conservation studies of historicphotographs as well as characterization of pre-Hispanic turquoisesand green stone objects.

The SANDRA system provides outstanding information formaterials identification and use of materials, technological studiesand for conservation and restoration purposes.

Under the actual configuration of the SANDRA system, the Moand/or Rh X-ray tubes combined with the Si-PIN detector is themost appropriate setup for a first general study. The combinationof detectors and X-ray tubes provides complementary informationfor cultural heritage with a convenient set of detected elementsand X-ray energy ranges.

This device represents a suitable choice using low costsemiconductor X-ray detectors and standard X-ray tubes. Thisfact has to be considered for limited budgets like in the case ofLatin American countries.

Acknowledgements

This research is part of the interdisciplinary Mexican project MOVIL:Non-destructive methodologies for the In situ Study of the CulturalHeritage supported by CONACYT Mexico grant U49839-R. Theauthors thank K. Lopez, J. Beristain, J. G. Morales and J. C. Pinedafor their technical support as well as E. Hernandez Vazquez forthe de la Cruz Badiano codex and the gold and silver artifactsphotographs.

The study of gold and silver pre-Columbian items was carried outin the Museo Regional de Oaxaca, Oaxaca, Mexico with the collab-oration of the INAH Center Oaxaca and the Conservation MetalsWorkshop of Escuela Nacional de Restauracion, Conservacion yMuseografia (INAH), as well as the Instituto de InvestigacionesAntropologicas and Instituto de Investigaciones Esteticas, UNAM.The studies of Mexican codexes were carried out in collaborationwith the Biblioteca Nacional de Antropologia e Historia, INAHand Laboratorio de Diagnostico de Obras de Arte of Instituto deInvestigaciones Esteticas, UNAM.

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