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Investigation, Enforcement andProtection Sector

Fingerprint Development andImaging Newsletter: Special EditionFebruary 2006

In this issue-

THE POWDERS PROCESS, STUDY 2:

Evaluation of Fingerprint Powders on Smooth Surfaces

AUTHORS

Helen L Bandey Andrew P Gibson

EXECUTIVE SUMMARYThis newsletter is the second in a series ofreports to provide guidance to scene examinerson the powders process. It concentrates on theperformance of the most commonly usedpowders on the most commonly occurringsmooth surfaces – both identified from a recentsurvey of scene examiners. The objective is:

• To ascertain if there is a significantdifference in the performance of fingerprintpowders on smooth surfaces encountered atscenes of crime.

Approximately 11,000 marks were developedwith the fingerprint powders on glass,ceramics, painted metal and gloss paintedwood. The developed marks were graded onthe surface using a scheme based upon theamount of developed ridge detail.

It is our intention to report on best practice forpowdering on textured surfaces orlifting/imaging of the developed mark in futurenewsletters in this series.

Results suggest that the effectiveness of thepowder is very surface specific; however flakepowders generally outperform granular oneson smooth surfaces. The study also highlightedthe importance of good technique whenapplying the powder as the number of marksdeveloped is very dependent upon the care andattention taken by the scene examiner.

Based upon the results in this trial the followingrecommendations are made:

• Scene examiners must receive appropriatetraining and maintain good applicationtechnique when applying powders. This islikely to be as important as powder selectionfor some smooth surfaces.

• Glass should be powdered with aluminiumpowder unless contamination prohibits itsuse.

• Magnetic powders should be used on surfacesthat are not perfectly smooth.

Publication No. 08/06

Figure 1: Application of magneta flake

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INTRODUCTIONHOSDB has been tasked by the FingerprintDevelopment and Imaging User Group toprovide scene examiners with guidance on themost effective powdering techniques for use atscenes of crime. Due to the vast quantity ofproducts (brushes, applicators, lifting mediaetc) on the market, HOSDB is not able toevaluate each individual product. Instead, aseries of newsletters is being issued that reporton best practice for commonly used techniques.

In order to have an accurate picture of currentpowdering practice, in 2004 HOSDBconducted a survey of scene examiners andprocurement departments within each policeforce in the UK. Responses, 208 in total, werereceived from scene examiners from 29 policeforces and 23 procurement departmentsreplied. Information was gained about whichtypes of powder were used, how often theywere used, how they were applied, to whichsurface it was applied, etc. The survey resultswere a valuable source of information and willbe referred to throughout this newsletter.

STUDY 1: ALUMINIUM POWDERIn August 2004 the first of this series ofnewsletters was published (Publication No.54/04 – Study 1: Evaluation of Fingerprintbrushes for Use with Aluminium Powder)*. Itconcentrated solely on the use of aluminiumpowder, predominantly because it is the mostwidely used powder in the UK and believed tobe one of the most sensitive on smoothsurfaces. This study demonstrated that thenumber and quality of marks found wasdependent upon the scene examiner’s choice ofbrush, with glass fibre brushes outperformingothers.

The survey was conducted at about the sametime that the results from Study 1 werepublished. Interestingly, 48% of aluminiumpowdering was performed with the top threebrushes (glass fibre, Tetra washable and squirrelzephyr) recommended in that study (see Table1).

The survey also indicated that 18% ofaluminium powdering was performed with a

squirrel mop brush. This brush is traditionallyused to apply granular powders. Of the brushestested in Study 1, this was shown to be leasteffective when applying aluminium powderand should not be used.

No adverse health effects were associated withthe use of glass fibre brushes or aluminiumpowder.

STUDY 2 – POWDERS ON SMOOTHSURFACESObjectiveAluminium powder is reported in the literatureto be one of the most effective fingerprintpowders on smooth surfaces. However it isunknown how much better it is, if at all, thanother powders. Does powdering one smoothsurface give the same results as powderinganother smooth surface, and what do weactually mean by ‘smooth’? To our knowledge,there has never been a study that has looked atthis basic problem, yet ~50% of fingerprintidentifications come from powders at scenes ofcrime – the majority of which were developedon smooth surfaces. Therefore, the objective is:

• To ascertain if there is a significantdifference in the performance of fingerprintpowders on smooth surfaces encountered atscenes of crime.

HOSDB plans to follow this with two furtherstudies. Study 3 is a continuation of Study 2 butmoves away from the more commonlypowdered surfaces and concentrates on surfacesthat are generally considered difficult to

HOSDB Fingerprint Development and Imaging Newsletter February 2006

Brush Average % of aluminiumpowdering performed with

brush

Glass Fibre 24%

Tetra Washable 9%

Squirrel Zephyr 15%

Other 34%

Squirrel Mop 18%

Table 1: Brush selection by scene examiners forapplying aluminium powder (from Survey)

* Can be accessed at www.hosdb.homeoffice.gov.uk

HOSDB Fingerprint Development and Imaging Newsletter February 2006 3

powder e.g. textured laminates, melamine, u-PVC. Publication of this newsletter is plannedfor summer 2006.

The survey data indicated that there is a widevariation in the lifting and imaging offingerprint powders at scenes of crime. 90% ofaluminium powder users lift the mark. Thisdrops to 74% for magneta flake and 64% forblack granular powder. A variety of liftingtapes are used along with a variety of ways ofimaging the lift. Each step has an effect on theoverall quality of the final mark. The liftingand imaging issues will be studied as Study 4 ofthis project following input from practitioners.

POWDERS AND THEIR APPLICATIONThere are hundreds of fingerprint powdersavailable for purchase from forensic suppliersthat can be used to develop marks at scenes ofcrime. The majority can be grouped into asmall number of categories relating to theirchemical composition, particle size or shape.Each category has its own characteristicsregarding its method of application to a surface,how it interacts with the latentfingerprint/surface and its visibility.

Examples of flake powders include aluminium,brass and magneta flake. These smooth metallicflakes lie flat on the surface causing thedeveloped marks to be highly reflective. Thedeveloped ridge detail tends to be continuous.

Black fingerprint powder consists of granularcarbon particles. The ridge development can beheavier around the sweat pores giving theappearance of a dotty mark. There are manyvariations of this type of powder such as jetblack and grey fingerprint powder. These arepredominantly carbon-based powders withsmall percentages of other powders added tochange the colour. It is unknown if thesepowder mixtures are more effective than thepure powder.

Magnetic powders are not applied with a brush;instead, a magnetic applicator picks up thepowder to form a brush head which is sweptacross the surface. The powders come in twoforms: the first is a one component powderwhere the magnetic particles act as thedeveloping powder; the second is a two

component system where the magneticparticles act as a carrier for non-magneticpowder. As with granular powders, magneticpowders can vary in colour as a result of addedcomponents.

Table 2 shows the extent to which fingerprintpowders are used at scenes according to thesurvey. The column highlighted in yellow isthe product of the first two columns andrepresents the overall usage of the powder. Itcan be seen that aluminium, magneta flake andblack granular powders account for themajority of powder used at scenes of crime. Allother powders such as fluorescent, bichromatic,fluorescent magnetic etc, are used infrequentlyand in total account for only 10% of allpowdering. According to the survey most ofthis powdering is conducted on problematicsurfaces where texture or colour may causedifficulty in developing or seeing the mark.Small trials at HOSDB have shown that mostof these powders offer no advantage over thecommonly used powders on the majority ofsurfaces powdered (i.e. smooth surfaces)although it is acknowledged that they may beinvaluable in specific situations. The onlyexception to this is black magnetic powderwhich proved to be an effective fingerprintpowder in the trials.

Therefore, powders used in this study were:aluminium, magneta flake, black granular andblack magnetic. The survey also showed thatthe main application of white powder was onvehicle paintwork; therefore it was included inthe trial on painted metal.

% of sceneexaminersusing thepowder

Average % ofpowdering

done byscene

examinersusing thepowder

Average %of

powderingdone usingthe powder

Aluminium 95 76 72

MagnetaFlake

49 25 12

BlackGranular

80 8 6

Others - - 10

Table 2: Popularity of commonly usedfingerprint powders (from survey)

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Aluminium Flake and Glass Fibre BrushFrom Table 2, it can be seen that aluminiumflake powder is used much more frequentlythan any other powder (72% vs. 12% formagneta flake). In fact it is used by 95% ofscene examiners and purchased by all forces. Itis predominantly used on smooth surfaces, themost common of these being glass, paintedmetal, ceramics and gloss painted wood. Table3 shows the percentage of aluminiumpowdering on each surface. 98% of glasspowdered at scenes is done so with aluminium.This drops to between 55-62% for the otherthree surfaces.

Two grades of aluminium flake powder can bepurchased from UK forensic suppliers underthe generic name ‘aluminium powder’. Bothgrades (Super 8000 and Offset 901) aremanufactured by Wolstenholme InternationalLtd and differ slightly in particle size (4-6µmand 7-10µm respectively). They both have a 3-5% w/w stearic acid coating. A recent HOSDBtrial indicated that there is no differencebetween them in terms of the quality of thedeveloped marks. Super 8000 aluminiumpowder was used throughout this study (SeeFigure 2).

Aluminium powder was applied with astarched glass fibre brush (Figure 3a) as it wasfound to be the most effective method ofapplication in Study 1. This is a LightningPowder Co. product and can be purchasedfrom most of the UK forensic suppliers. Thepowder was applied with a light brushingaction and the mark was gradually built up asdescribed in the MoFDT*. Spinning the brushoffered no advantage. 48% of aluminiumpowder users reported that they sweep/cleanout over-developed marks. The most popularbrush for this is the squirrel mop brush (Figure3b).

Magneta Flake and Magnetic ApplicatorThe survey suggests that magneta flake is thesecond most widely used powder. It accountsfor 12% of all powdering and is used byapproximately half of the scene examinerssurveyed (See Table 2). It is used on a widerange of surfaces including both textured andsmooth.

The powder is a single component magneticpowder where the powder serves as both thecarrier and developing medium. It wasdeveloped in the 1991 by James et al** as partof a joint project between the Home Office and


Surface Glass PaintedMetal

Ceramic GlossPaintedWood

% of surfacestreated withaluminium

powder

98% 62% 58% 55%

Table 3: Aluminium powder use on the fourmost commonly powdered surfaces (fromSurvey)

Figure 2: Scanning Electron Microscope (SEM)image of aluminium flake fingerprint powder(Super 8000)

(a) Starched glass fibre brush

(b) Squirrel mop brush size 16

(c) Magnetic applicator

Figure 3: Powder applicators used in this study

* V.Bowman Ed., Manual of FingerprintDevelopment Techniques 2nd ed. 1998, Revised 2001and 2004

** James J.D, Pounds C.A. and Wiltshire B., Journal


the University of Swansea. It is now producedexclusively by CSI Equipment Ltd, although itcan be purchased from other suppliers. It isproduced by milling spherical carbonyl ironwith 3-5% stearic acid in an appropriate solventto produce a smooth edged flake with a particlesize varying from 10-60µm (see Figure 4). Aswith aluminium powder it is extremelyreflective.

There are many magnetic applicators sold byforensic suppliers and little work has beencarried out to assess the performance of each.The most commonly used applicator identifiedin the survey was ‘magnetic powder applicator’from WA Products and consequently was usedin this study (see Figure 3c).

The powder is applied by sweeping a loadedapplicator across the surface. One sweep shouldbe enough for development however multiplesweeps are sometimes required. It is quitecommon for heavy marks to be over-developedand removal of the excess powder can beachieved by either passing a loaded or unloadedapplicator over the area of interest or sweepingout the mark with a suitably soft brush. In thistrial a size 16 squirrel mop brush was used asthis was the most commonly used sweeping outbrush identified in the survey. It should benoted that some marks can be destroyed by anyamount of sweeping out.

Black Granular and Squirrel Mop BrushAccording to the survey, black granularpowder is used by the majority of sceneexaminers (80%), but only accounts for 6% ofpowdering at scenes (Table 2). It is commonlyused on both textured and smooth surfaces.

Most black fingerprint powders are carbon-based. The main carbon manufacturer in theUK is Cabot Ltd. They currently supply mostof the forensic suppliers with Elftex 415 carbonpowder. This elemental carbon has a particlesize of 5-10mm and can appear textured andirregular in shape (see Figure 5).

There are many modified versions of blackfingerprint powder. They generally have asmall percentage of dye or other chemicaladded to the carbon in order to change thecolour slightly. It is not believed that thesemodifications to the carbon powder will alterits effectiveness. This study will only determinethe effectiveness of Elftex 415 carbon powder.

As far as we are aware no studies have beenconducted on the method of application ofgranular powders. Traditionally black granularpowder is applied with a squirrel mop brush.Survey results suggest that 72% of sceneexaminers currently apply this powder with asquirrel mop brush, with size 16 being the mostcommon. This brush was used in the study andthe powder was applied as described in theMoFDT Section 7.3. Overdeveloped markswere brushed out with a clean size 16 squirrelmop brush.

Black Magnetic and MagneticApplicatorOf the powders chosen to be studied in thistrial, black magnetic powder is the least usedaccording to the survey. It is predominatelyused on textured surfaces.

It is not similar (chemically or physically) to

Figure 4: SEM image of magneta flakefingerprint powder

Figure 5: SEM image of black granularfingerprint powder

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the other powders used in the trial. It consistsof large magnetic carrier particles of iron (20-200µm) and smaller non-magnetic particles ofiron oxide, Fe3O4 (3-12µm) (see Figure 6). Thelarger particles act as a carrier medium for thesmaller particles which adhere to thefingerprint residue thus developing the mark.Discussions with suppliers indicate that theirsupply of black magnetic powder wasmanufactured by BVDA, Holland.

This powder was applied with the magneticpowder applicator from WA Products in asimilar way to magneta flake in the study.

White Granular and Squirrel Mop Brush

Data from the survey suggests that whitepowder is used on wood most frequentlyfollowed by vehicle paintwork (although its useis still considerably less than aluminium on thissurface). It is used infrequently on glass,ceramics and painted doors and so will only be

evaluated on painted metal in this study.Powder effectiveness on wooden surfaces willbe reported in the next newsletter.

EXPERIMENTALLaboratory Control MethodsAll of the powdering was carried out in aBassaire SPL 4 RFM powdering cabinet with aflow rate across the sash in excess of 0.3 ms-1.

Test SurfacesThe survey suggested that the most commonlypowdered surfaces at scenes of crime were glass,painted metal (vehicles), ceramic and glosspainted wood and so were used in this study.

A4 size toughened glass was purchased from aglazier. A variety of kitchen/bathroom ceramictiles were purchased from DIY stores. Secondhand white/cream gloss-painted doors wereobtained. These doors were removed from aproperty prior to new doors being fitted and sohave unknown history. They were then cutinto A4 size. A4 size sheets of steel weresprayed with car paints including allundercoats. The two colours chosen were red(‘Vauxhall Flame Red’) and metallic blue(‘Vauxhall Breeze Blue’). The metallic blue, aswith all metallic cars, was coated with anisocyanate lacquer layer. The surfaces werecleaned with laboratory detergent followed bythorough rinsing. The surfaces weresubsequently wiped with ethanol.

Fingerprint DonorsFingerprint donors were selected from a poolof staff members at HOSDB. For each trial atleast twelve donors were selected. It wasimportant to obtain planted marks from a widerange of donors so that the chemicalcomposition and quantity of the mark residuevaried considerably.

Fingerprint DonationFor all laboratory trials a HOSDB standardprotocol was followed for the collection offingerprints from donors. Donors used had notwashed their hands for at least thirty minutesprior to donating prints. This allowed adequatefingerprint residue to collect naturally on thefingers. In line with all HOSDB experiments,donors were asked not to rub their fingers


Figure 6: SEM image of black magneticfingerprint powder

Figure 7: SEM image of CSI Ltd ‘instant white’fingerprint powder


across the face, hair etc just prior to donating,as this increases dramatically the amount oflatent material (predominantly sebaceous) onthe fingers and is considered unrealistic.

Donors were asked to rub their hands togetherin order to get an even coating of naturalsecretions and/or contaminants across thefingers before depositing marks in a depletionseries.

The following three experimental methods areused at HOSDB to compare processes: (1)comparison of split marks; (2) comparison ofalternate marks within a depletion series; and(3) comparison of different depletion series.These methods are explained in detail in theAppendix. The majority of the experimentswere conducted using the third option, withthe exception of gloss painted wood for whichthe second option was used.

DevelopmentAfter ageing for either 1 day or 1 week, theappropriate depletion series were powderedwith aluminium flake, magneta flake, blackgranular, black magnetic or white powder(only for painted metal). Different staffmembers from the fingerprint group, who haddeveloped expertise in powdering at HOSDBrepeated the trials as the effectiveness of thepowdering process can be very user dependent.It should be noted that it was not alwayspossible to repeat the trials as planned, due tostaff member availability.

Grading the FingerprintsThe aim of this study was to determine theeffectiveness of the powder in terms of thequality of the mark that it developed on thesurface. As a consequence, none of the marksdeveloped in this study were lifted or imaged.Instead they were viewed using appropriatelighting and optical devices and graded from thesurface.

In order to assess the performance of eachpowder a suitable grading scheme had to bedevised. A grade was given to the markdepending upon the quantity of clear ridgedetail, taking into account the continuous ridgeflow and Galton features. The grading system isdescribed in Table 4.

Trial SizeAs discussed in Study 1, there are many factorsthat affect the performance of the powderingprocess. One way to reduce the chances ofspurious results (especially for variables out ofour control such as age of latent marks, donor-donor variation, and donor-time variation) is tocarry out large studies to give meaningfulconclusions. As there are so many variables itis clear that a trial can very quickly becomeextremely large – in this work 11,568fingerprints were studied (see Table 5).

Grade Comments

0 no development

1 signs of contact but < 1/3 of markcontinuous ridges

2 1/3-2/3 of mark continuous ridges

3 >2/3 or mark continuous ridges, but notquite a perfect mark

4 full development – whole mark clearcontinuous ridges

Table 4: Grading system used for determiningthe quality of ridge detail for developed marks

Number ofgraded marks

Glass 1,296

Painted Metal 4,800

Ceramic 2,880

Gloss Painted Wood 2,592

Total 11,568

Table 5: Total number of fingerprintsdeveloped in this trial

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RESULTS AND DISCUSSIONThe results for each surface are presented anddiscussed individually. Each data set ispresented as bar graphs showing the percentageof marks with greater than a third ridge detail(i.e. marks graded two, three or four) for eachpowder and age. This was selected as a markgraded either 0 or 1 was considered unlikely tohave sufficient detail for identification. Thedata in the graphs is averaged across all donorsand evaluators. There are many practicalfactors, such as ease of use, visibility etc thatinfluence the scene examiner’s choice ofpowder. These are difficult to quantify but arecrucial to the successful use of a powder. Theresults show only small differences inperformance of some of the powders and sothese other factors become increasinglyimportant and are discussed throughout thissection. Table 6 summarises the advantages anddisadvantages of each powder.

GlassThere are few in-depth comparisons offingerprint powders in the literature. Thosethat do exist quite often use glass as the testsubstrate as it is most frequently encountered atpoints of entry or on vehicles. It is alsoconsidered to be an ideal smooth surface onwhich to test powders as it normally gives littlebackground development and is very smooth.

This was the smallest trial in the study with 432marks being developed and graded by threedifferent staff members – totalling 1296 marks.The three staff members conducting the trial allproduced similar results for the relativeperformance of the powders. These results arecombined and presented in Figure 8, whichshows that aluminium powder is the mosteffective powder, developing 96-99% of theplanted marks. Magneta flake did not performas well as aluminium but was more effectivethan the two non-flake powders whichdeveloped approximately 20% fewer marksthan aluminium.


Table 6: Advantages and disadvantages of fingerprint powders

Powder Advantages DisadvantagesAluminium • easy to app ly

• very sensitive• reflective• good continuous ridge detail• generally does not give much

background development

• can be difficult to see therefore mark canbe missed (especially on a reflectivesurface)

• a good torch must be used to see themarks – especially the faint ones

MagnetaFlake

• very reflective• easy to see – good contrast• Once developed they are easier to see

than aluminium

• application is not straightforward – had todo several passes in areas due to thepowder brush not making contact in allareas

• more infill between ridges than aluminiumalthough the contrast is still very good

• brushing out often necessary for heavymarks

• light marks can be removed when brushedout

BlackGranular

• easy to see• It is very effective on m arks from heavy

donors, where flake powders mayoverdevelop

• Good contrast

• less sensitive than flake powders on glass• marks can be dotty making it more difficult

to see clear continuous ridge detail• very messy

BlackMagnetic

• good quality continuous ridge detail• Generally it does not require sweeping

out

• Poor contrast for weak marks• Some background development


The results suggest that on glass the flakepowders are slightly more sensitive than thenon-flake ones. Aluminium was marginallymore effective than magneta flake.

Applying aluminium powder was relativelystraightforward compared to magneta flake.The brush was loaded sparingly with powderand applied to the surface with a sweepingmotion allowing the mark to build upgradually until optimum development wasacheived. Magneta flake, on the other hand,required considerably more skill. The first passof the loaded magnetic applicator frequentlyoverdeveloped the heavier marks. Thedeveloped lighter marks also had interferencefrom background development. The excess ofdeposited powder was removed as described onpage 4. This was very successful for heavymarks leaving clear ridge detail; howeverlighter marks were quite often destroyed. Forthis reason, all of the marks developed withmagneta flake were graded before and aftercleaning out and the best score was included inthe results.

Working and best practices for glass appear tobe in line as the survey indicates that 98% ofglass is already powdered with aluminium.

Painted MetalThis was the largest trial in this study with 2400marks being developed and graded by two staffmembers – totalling 4800 marks. As for glass,only small differences were observed betweenthe two staff members and their overallconclusions were the same. The effectiveness ofall of the powders on the non-metallic painted

metal was greater than on the metallic paintedsurface; however the relative performances ofthe powders were similar.

The results for the painted metal trial arepresented in Figure 9. It shows that whitepowder is considerably less effective than theother four powders developing considerablyfewer identifiable marks. This is due to thelower sensitivity of the powder rather thanbackground interference, ridge infill orapplication difficulty. This was identified by aquick drop off in development down thedepletion series resulting in light marks beingmissed. This concurs with earlier HOSDBstudies and reinforces why it was not chosen tobe trialled on the other surfaces.

The other powders follow the same trend as forglass with the exception of aluminium powder.Surprisingly, the amount of identifiable marksdeveloped with aluminium falls to levels similarto those from the granular powders. However,magneta flake continues to outperformgranular powders.

A limitation of aluminium powder is visibility,especially if applied to reflective surfaces suchas vehicles. In normal circumstances thesemarks would be lifted and imaged without thebackground reflectivity interfering with thequality of the mark. In this trial all marks weregraded on the surface and as expected thisproved to be more time consuming thangrading other powders due to the low contrast.However with appropriate angled lighting andmagnification all developed ridge detail couldbe viewed.

Figure 8: Effectiveness of fingerprint powderson glass

Figure 9: Effectiveness of fingerprint powders onpainted metal

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Magneta flake, although developing a higherpercentage of marks than all of the otherpowders trialled was difficult to apply. As withglass, heavy marks tended to fill in requiringcleaning out with either the magnet or a brushin order to develop the best mark. Light markscould easily be removed if this cleaning outprocess were performed.

CeramicFor the ceramic tile study 1440 marks weredeveloped and graded by two staff members –totalling 2880 marks. Although there wereminor difference between the staff membersand type of tile, overall there was very littledifference between the four powders as can beseen in Figure 10.

On the ceramics tested, neither of the flakepowders appeared to be any more sensitivethan the granular powder. The powders appliedwith a brush tended to give less backgrounddevelopment than those applied with amagnetic applicator, however this did not affectthe number of identifiable marks developed.

Gloss Painted WoodGloss painted doors are one of the mostcommonly powdered surfaces at scenes and aretreated by many scene examiners withaluminium powder (see Table 3). The surfacecan quite often show brush marks where thepaint has been applied. For this trial, one of thedoors had clear brush marks whilst the otherhad a texture as though the paint had beenapplied with a roller.

2592 marks were developed and graded by onestaff member. As stated in the ‘fingerprintdonation’ section of this newsletter, a newmethod (method 2) was trialled to assess thepowders and is described in more detail in theAppendix. This method offers one mainadvantage over the other method usedthroughout this report – it is comparing theeffectiveness of processes on marks taken fromthe same depletion series. These marks will becloser in chemical composition than thosetaken from different depletion series giving agreater level of confidence hence the need forfewer trial repeats. The main disadvantage ofthis method is that it only allows for thecomparison of two processes. In this trial fourpowders were being tested therefore the trialwas divided into halves. The first half comparedthe two flake powders, whilst the second halfcompared the two granular powders.

From Figure 11 it can be seen that magnetaflake and black magnetic considerablyoutperformed aluminium powder and blackgranular respectively. In both cases, the powderapplied with a magnetic applicator developedmore marks than those applied with a brushirrespective of the particle size, shape andsurface type. This was predominantly due tothe brushes preferentially developing surfacetexture rather than ridge detail. Additionally,the granular powders (black and blackmagnetic) both gave uniformly highbackgrounds. These two factors were key todetermining the effectiveness of the powders onthis surface.


Figure 10: Effectiveness of fingerprint powderson ceramic

Figure 11: Effectiveness of fingerprint powderson gloss painted wood showing (a) aluminiumvs. magneta flake, and (b) black magnetic vs.black granular


The two magnetic powders were then trialledagainst each other the results of which areshown in Figure 12. Magneta flake slightlyoutperformed the black magnetic powderacross both ages of mark.

CONCLUSIONSThis study has highlighted the importance ofappropriate training and subsequent goodtechnique when applying fingerprint powders.All of the powders tested in this trial areapplied differently and maximising the numberand quality of marks developed is verydependent upon the care and attention takenby the scene examiner. Magneta Flake, forexample, performed very well across allsurfaces, but if applied hastily and not cleanedout appropriately a large percentage of markswill be missed or destroyed.

This study also demonstrates the importance ofselecting the right powder for the surfacepresented to the scene examiner. There is notone powder that is clearly the most effectiveacross all of the surfaces examined in this study.For glass, aluminium powder is still consideredto be the most effective powder and is easy toapply. The results were less clear-cut forceramics and painted metal. The gloss painteddoors used in this study, although consideredsmooth, were actually slightly textured due tothe paint application. This slight texture wasdeveloped with powders applied with a brushmaking it difficult to see the mark.

RECOMMENDATIONSBased upon the results in this trial the followingrecommendations are made:

• Scene examiners must receive appropriatetraining and maintain good applicationtechnique when applying powders. This islikely to be as important as powder selectionfor some smooth surfaces.

• Glass should be powdered with aluminiumpowder unless contamination prohibits itsuse.

• Magnetic powders should be used on surfacesthat are not perfectly smooth.

FEEDBACKFeedback from Study 1 was positive, withmany scene examiners adopting the advicegiven.

We would be very interested to hear from sceneexaminers who have made a change in workingpractice or will do so in the future based uponthe newsletter results.

ACKNOWLEDGEMENTSThank you to all of the scene examiners andprocurement staff who took the time to fill inthe survey. Thank you to the scene of crimeequipment suppliers and powder manufacturersfor their time and assistance.

Figure 12: Effectiveness of fingerprint powderson gloss painted wood showing magneta flakevs. black magnetic

12

APPENDIXThe following methodology is used for mostexperimental trials of fingerprint developmentprocesses at HOSDB:

Option 1: Split Marks DepletionFigure 1A outlines the necessary steps forcomparing processes using split marks. Once adepletion has been deposited it is cut in half andeach side is processed with a different techniquebefore being reassembled for comparison. Thisis then repeated, but the side of the markdeveloped with the processes reversed. Thiswill reduce the effect of any pressure differencesthat may have occurred when depositing themarks.

Stage 1: Follow steps 1-4*

Stage 2: Repeat, but development reversed*

* Note: steps 1 and 2 can be reversed

Figure 1A: Option 1 Methodology

If possible, this should be the method of choiceas it directly compares half marks with thesame chemical composition, quantity andpressure. However, it is only suitable onsurfaces that can be cut cleanly into strips (e.g.adhesive tapes, plastic bags, paper etc). It is notsuitable for processes that may have ‘edgeeffects’ such as powders and thus was not usedin this study.

Option 2: Alternate Marks DepletionFigure 2A outlines the necessary steps requiredfor comparing processes using marks from thesame depletion series. Donors are asked todeposit marks in positions 1,2,3 etc until therequired length of depletion is reached. Onesurface will then contain the odd numberedmarks in a depletion and the other the evenmarks. These are then processed and compared.It is important to repeat the steps but reversingthe development process used on the odd andeven numbered marks. This will remove anyfavouring of techniques based upon whichmarks are developed.

Stage 1: Follow steps 1-2

Stage 2: Repeat, but development reversed


This method can be used if comparing twoprocesses. Although not directly comparing thesame mark, Option 2 allows for a comparisonof marks from the same depletion series. Themarks will have similar chemical composition,quantity and pressure although this is not as


Step 2

Process X Process Y

Step 3

1

2

3

4

i

Combine

Step 4

1

2

3

4

i

Step 1

1

2

3

4

Deposit Cut

1

2

3

4

ii

Step 2

Process X Process Y

Step 3

1

2

3

4

i

Combine

Step 4

1

2

3

4

i

Step 1

1

2

3

4

Deposit Cut

1

2

3

4

ii

Step 1

1

3

5

7

i

Deposit

2

4

6

8

j

Deposit

Step 2

1

3

5

7

i

Process X

2

4

6

8

j

Process Y

Step 1

1

3

5

7

i

Deposit

2

4

6

8

j

Deposit

Step 2

1

3

5

7

i

Process X

2

4

6

8

j

Process Y


tightly controlled as in Option 1. This methodis suitable for all surfaces. However it is notsuitable if comparing more than three processesdue to the length of depletion series required.

Option 3: Different DepletionsThis is the simplest of the methods used tocompare marks. In this case different depletionsare processed entirely with different processesas shown in Figure 3A.

Stage 1: Follow steps 1-2 (repeat)


This should be the method of choice if Options1 or 2 cannot be used. In this case marks withinthe same depletion are not compared. Instead,depletions from the same donor are compared.The marks will have greater variability thanthose in options 1 or 2 although this is still anexcellent method for comparing processes. It issuitable for all surfaces and processes, however,more data will be required due to the greatervariability introduced by using differentdepletion series.

Step 1

1A

2A

3A

4A

iA

DepositDepletion A

1B

2B

3B

4B

iB

DepositDepletion B

Step 2

Process X Process Y

1A

2A

3A

4A

iA

1B

2B

3B

4B

iB

14 HOSDB Fingerprint Development and Imaging Newsletter February 2006

16

CONTACTS

HOSDB Investigation, Enforcement andProtection SectorFINGERPRINT DEVELOPMENT AND IMAGING

Valerie Bowman 01727 816209Vaughn Sears 816216

Helen Bandey 816385

Alex Hart 816304

Stephen Bleay 816252

Andrew Gibson 816272

Lesley Fitzgerald 816433

Sales of Fingerprint Publications and IRISSystems

Erin Wheeler 816454

FAX 816253

ADDRESS

Home Office Scientific Development BranchSandridgeSt AlbansHertfordshireAL4 9HQUKwww.hosdb.homeoffice.gov.uk


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