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823

PJl.O: IDENTIJ:i'ICA.'J'ION 01~ INKS

A Systematic Approach to Ink Identification B~' ~.!CHARD L. BRUNJ!:LI,:E and MAYNARD J. PRO (Alcohol, Tobacco and Firearms DiVISion, Interned Revenue Service, Washington, D.C. 20224) A systematic approach to idcn tificution of writing inkA is p•·cscntcd. This approach UACA a ~ultiplc technique method for analysis of the Inks to dc,•clop a hu·gc number of idcntiliahlc points fo1· comparison. Well established methods nrc used for the analysis of inJ~s ~;uch as , 1. tun luym· chromatography, spcctrophotOJnc.try, und gus-liquid chron1atogr·uphy, in uddiLto~ to truditiouul 1ncthods for comparison ~vluch usc ultr·aviolcl and infrared light. The Hilts nrc identified hy comparing the results of tiJC questioned inks with results obtained from n complete library of wr·iting inks maintained by this luboralory. lly using the described approach, most inlu; can be identified with a high degree of cct·tuin ty.

Prior to 1950, inks on que~tioned doeumenb were t>xnminc•,[ !Jy ohsrn·ing lhr rolor under waye]rngths of li!!;ht ranging from uh.r:ncioirt to in_fmrPd. Tlw~P trelmiquPs wC'rr supplementf'rl With photogmphy usin!!; :-rlt>et.ed liilf'rs. ('Jwmieal spot lr:<ts \\'('!'(' abo usNl to drtrrt mrtal=< ;:ueh a:" iwn. eopprr, nmadium. nnd C"hromium. Although these methods helped to distinguish between ma~y types of inks, it was not possible to ·cbaractenze the various formulations. The development of more advanced techniques for analyzing inks was slow because even the more sophisticated analytical approaches required the destruction of small portions of the questioned document. However, during the past few years the cotnts have accepted the practice of removino"' very small samples for analysis. Somerford and Souder 0) analyzed fluid writing inks by paper ch.romatography. Their work showed that only a mtcro-quantity of ink was needed for the analysis and t.hat destruction to the document exam.ined was minimal. By 1052, ballpoint inks began to appear on the market in significant numbers. Brown and Kirk (2) showed that electrophoresis can be employed to separate dye components of these inks. In their work this technique was compared with paper chromatography and it was reported that electwphoresis could be used to separate constituents not amenable to separation by pnpe1· clu·omatogmphy. Following this work, numerous studies

comparing paper chromatography and electrophoresis and describing various solvent systems for use in the development of paper chromatograms were reported (3-8). In 1960, Tholl (9) applied thin layer chromatography {TLC) to ink analysis and found that the technique coul.d he used effectively to separate dyes and other components of writing inks. This analytical tool was found to be particularly suitable for the examination of micro-quantities of ballpoint inks and made possible the separation of dye mixtures. :\IacDonell (10) showed that it was possible to rhamet.f'rize fountain pen inks by porous glass rhromat<Jgraphy and electrophoresis. This approach permitted separations under a much wider r.ange of rondition~ than found in paper cbromat{)graphy and electrophoresis because th.e final separations take place in an optiesily transparent medium which allows direct spectral measureml'nts of the separated components. Crmm et a.l. (11) studied blue ballpoint inks and I'<'[Jorted a scheme of analysis for tb.e identification of these inks by their dye compositions. This work showed that blue ballpoint inks could be divided into several distinguishable categories, depending on the dyes present. Nakamura and Shimada (12) reported TLC of ballpoint inks on a micro-scale from TLC plates prepared from rnicl'oscope slides. A sohrent system consisting of 50 parts n-butanol, 10 parts ethanol, and 15 parts distilled water was found to be effective for the majority of ballpoint inks. It was further shown that 4 spots from a single dye such as methyl violet could be separated with this system. Prior to about 1966, efforts were directed towards the development of new analytical methods to compare questioned and known ink samples; very little attention was given to identifying the somce of questioned inks or to establishing dates of prepa.ration of questioned entries. The dating of inks \Vas limited to the determination of periods of time when gross changes were mnde in the This paper wns presented at. the 85th Annusl Meeting of the AOAC, Oot. 11-14, 1971. ut \r>tshington, D.C.


824

.IOUHNAI, m~ 'L'tm AOAC

compm~it.ions

of ink. For l'xtunplr. tht' rhat\1?:<" from o\1-base soh·ents to glyt•ol bt>ses prodded 11 date prior to "·hich the glyrol ballpnint inks did not exist. Early E'fforts WE'I"t' mttdf' to idl'ntify inks for thl' pmpose of dating (Hofmann, \\". (1969) pl'ivat.E' communiration). Hofmann rolleded bnllpoint ink formulations from n number of manufartml'rs anrl the rt-sult.s of his work indimtt-d that qnt:-=-timwd inks Cl111 be- idt-ntifit>cl and datl:'d if n e:-tmpL•tl' rollertion of inks and tht-it· pmdurtion dnt~·s nrC' obtained. Hofmann's analytira1 prol'E'rlurrs in,·oh•ed papt>r rhmmntography aud TLC' with ntrioussoln:.nt syste-ms. Ht> nhm us~d spl:'t'tt·oplllltomPtr:y, spot tests. aud thl' typiral nond£'8trul'th·p. tests to aid in thE' identifiration. Bast•d on hi~ work it was condndf'd that, although an ink l'nnnot bl:' absolutely idt-ntifid, its mnkl:' or idl:'ntity can be detl:'rmined with n great dt>nl of st•il:'ntiti.t• certainty. Hamman (13) l'P.portl'-Cl a nondestruetin' $pectrophotomett·ie method for thr id£>ntificatinn of inks and dyl:'~ on quC'stionrd rloeumf'nt:-: by analyzing the inks dirertly on thf' rloeumrnt without treatment. For the past se-,·p.rul yf'ars the Intl'rnal Rt>n•nut• 8en·iee ha:> carried out ron:<idl:'rablf' rr:-:~·:trdt in the fif'ld of ink a~mly:<i:;; in an attt>m;1t to nwf't thf' needs of the agency in the enforcement of its laws and regulations. In many instances, the date the document was prepared is extremely important and could be the basis for establishing fraud against the go\·ernment. Since well established techn.iques for identifying inks exist and a relatively complete ink library is now available, it is possible to determine the first production date of an ink formulation. The purpose of this paper if> to present a systematie approach that can be successfully u:;erl to compare and identify inks. Experimental

Questioned inks are identified by rompari~on with known standard inks. The following approarh ic; used: The document. to be examined should be photographed to maintain a record of the condition of the document upon rereipt. lA 1-1 blark-and-white ropy is sufficient.)

Visual and lYiicroscopic Examinations Examination uwlcT t•isiblc• lighl.-Thc ink on lhc document is observed visually with and without the aid of magnification lbinoeular ;;tercrJmierostope

(Vol. 55, No.4, 1972)

\ 10-·HlOX nmgnifie1ttiun) or mn.gnifying glnss (lOX)) to dl:'termine l;he typf' of ink u~ed (bttllpoin~, fibet·· tip, 1\amtain, f'tt•.), c·olor, nnd ovemlllitw qtutlity or lhe writ.ing. A mngnifil'ttlion of lOX is ;;uf!icient. Flfrm•iold nnd infrart•d light t•xaminalion..-'l.'ho ink is nb~Nved under both long- ttnd short.wn.ve ult.mvioll'l· light to clet.ennine whether t.he ink fluorest'I:'S • .Det.r~·minat.ion of the t•eln.tive optteity o( ~he ink to infrm·l:'d light involves viewing t.he ink Uwough an infra-red inmge rotwersion mierosrope (minimum or lOX mngnirienlion; Leit::~~, or equivalent). Writing inks >'how clilTerent degrees of lt·a.uspnrency or llptwity when viewed uncle•· infmred light.

Chel'nit•al Tesls Solullilii!tlfsls.-On(' or 2 plugs nf ink ore remO\•ed from thl:' written line with a blunted point (tip rul ()iT nnd end Hle1l) of a lwt>odermic needle (0.5 mm (Li11.nwterl. Tht> relative solubility of the questioned ink in vnrions solvents is det.ermined. Fibers t~ou­ tnining the ink IU"I:' sepamtecl nnd nb:-;olute ethnnol, l'tlumol-wntet· \I+ 1), distilled walet·, und pyridine are applied to the fibers l'ontaining the ink. The rc• snits are ~Jbs('rved with lOX nmgnHit·ntion. C'hol!imf .~pol lfsl.~.--OnC' or 2 plugs n•movc<l n.' deserihed nbov(' ure U"'<'d to d('!<'rmine whether any enlc>r !"('!WI ions m·c·ur upon nddition of HCI, I-hSO~. HX03, ami XnOH. Tlw lt'st.~ m·p ob.•erved at about

lOX. Thin Layer Chromalogrczphy About 1-10 plugs of ink are removed, depending on the quantity of ink deposited and the type or ink present;. The ink is dissolved in a minimum amount. of solvent, usually about 2 dmps. The solvent used to dissolve the ink is the one determined to be the best suitable for this purpose during the solubili1;y tests. The color of the ink solution is observed and recorded. The visible spectrum of the solution mny also be rerorded spe<"lroplmtometrically. The dissolved ink i!' then spotted on an Ji~nst.man precoatcd silica gel sheet (without indicator) with disposable 5 pi micmpipets. After the spol<~ n.re allowed to dry, the appearn.ucc at the origin is recorded. Then the rhromatogram is developed for 30 min in solvent system I (composition given below). After 30 min, the C'hromatogrnm is n.llowcd to dt"j' and the values of the various dyes pre::;ent o•· ultmviolcL fluores<"enl: spol:s observed nre cnlculat.ed. All of the inks fmm the Htnnclmd ink library which have $imilar dye <'om positions are selected for ronnlysis by visually comparing the chromnl:ogt·n.m of ·~he que~:~tionerl ink with thoHe from the known i11ks iu the library o.ncl by referenC'e tn the eodcd cards which contain !;he reHult.'i or all of the te11ts ca.l'l"icd

n,


w '' :iiJWNI•:LLI•: & l'HO: liH~NTflo'fCA'J'ION OF JNli:R I ink;;. The Htandanllibt·ary ·otJt on the ('Oiltro~ librnry Jr,,, • • 1\'' ~~

:i.nks nrc c•oded aeeonling lfl !:he following criteria: ~~· <{J) type of i11k, (2) ('olor of i11k, {;J) infmred opll;City, ft: ~4) l.ypc r~ud nllmber of dyer; pl'escnt, induding di!i-r\ per:.;ion r.ompon(•nl:;, and (fi) ultmviolet UuoreHeent '11 ' .oCOlliJlOllCJd:s.

•·.J The sclec•l.ecl s~nudnrd ink;; are annlyzed ~;nmulta­

~; neously with fbc quPslioncd ink on the snme TLC ~i tPiaLc. This TLC exn.mi11ttlion is rat-ried o11t on

.;a Mcrek prec·oaLed .~ili<·a

gel gla.'is plate;;, m;ing 2 difltenmt solvent liystem:; (:.;hown bel.ow). A develop·~ 'r mcnL til'ne of :l hr is Ll:>ed !oJ' these plates. Anulter·h . rpl'eronted silic·a. gel glu.~s plaLeH c•an al~o be llscd, but ~,the dc.welopment lim!' is on!)· :~o min. r.~

Proportion

70 :1:1

Et hylm·<'lair ;\.h:mllllt> ethtuwl I >i~l illPd wn!rr Ry.~tcm

11-Bul:uwl Ethauol ])i,-t iiJ(•d WILl Pl'

:m Il ;'j{)

.10 ].-,

The >-t>Jmmti .. u of 1h<· dy(•" into many di:-tim•gui><hnbll' rompnll!'lll" orl :\lprr·k :111d AnnllC'('h plniP:'< provides sev·eral points of comparison between questioned and known inks. The chromatograms al'e •obsm-ved under visible and ultraviolet light for ~ ·idenWiable eomponents. Visual ami mieTOscopic ~ •examinations and chemical tests are next carried out }.on the sdeded t'tandard in],;o; and the results are i rompared with the resnHs fm· the questioned ink. Sp.eclmpholornetry

The proredures described above are usually sufficient to eliminate all but perl1aps l or 2 of the t standard ink~. H more information is needed to distingui~h them, tllC' 1\Ierrk o1· Analtech TLC plates containing the :<eparated dye romponents of the questioned nncl known inks are seanned on a. spectrophotometer equipped wilh an atturhment for scanning spots on TLC plate:;;. Eneh blue ink is usually scanned in the visible region n.t 5;i0 nm, with n. xenon light source. The per cen~ transmission of light through e.a.ch s<:>purated dye component is rerorcled und the relative amount of CM]l dye pr.~sent with respert to the othl"t' is eal·rulnted. The waveh:mglh rhosc:on fm· scnnning vnries lWcording lo the enlor of the ink nnd depends on which dye:; an• pl'csent. A wavelength is rhosen so ~hal; each dyt- pn•sen1 n.b:mrbs t lw light' with l:'qunl Jnlensity.

825 Or.her· Exarninarions The procedure described above i<> usually sufficient to match a r;tandaz·d ink from the library with the questioned ink; however, wher.ever proprietary information from the manufacturer of the identified ink i;; known, it ill desirable, if possi.ble, to ch.eck the questioned ink fm· the presence of these known oomrJIJnents. This approaeh can provide additional points of identification. For example, ~here are a variety of fatty acids, resins, and viscosity adjusters added t{) inks, .and these compounds can be identifi.ed when a sufficient quantity of the questioned s:Lmple is available for analysis. In many cases, these components can readily be detected by gas-liquid chromatography (GLC) or by TLC. Carbon and graphite, which are common dispersion ingredients in reproduction ballpoint inks, can be distinguished b)' electron diffraction techniques. Graphite will! display a. specific elect1·ou diffraction pattern, but carhon will not because it is not a crystalline substance. Some ink-; contain materials that f!uoresoo and other llniquc eomp<Jnmis which help make an identification almostTabsolute when these materials are determined. The aut!1ors have not found any special advantage~ for electwphoresis over TLC for aJJtY of tbe variou.« types of writing inks. However, when suffi.r>ient iuk if' available for further ana]ysis, this meihod ('3.!1 provide another means of confirming the identification.

Discussion

The des·cribed systematic ap1Jroach to writj.ng ink identification has been used routinely at the Internal Revenue Service Laboratory since 1968 and seYeral hundred cases have beetl examined. Testimony based on this technique was given in Federal courts on numerous occasions and in some instances the ink testimony was used as primary evidence. In this work the questioned inks are identified with a. high degree of scientific certainty on the basis of this systematic approach. This is very much like eomparing pa.int, glass, and soil and utilizing points of identification to establish stt&tistically significant comparisons. It should be recognized that. it win never be possible to obtain every ink that, is produced in the '"odd, just as it would be impossible to obtain everv finO'erprint. or all paint$. For this reason, it is ~1ot l~ssible to identify 0very questioned ink submitted for analysis. Fnrtl1er, absolute jdentificn.t.ion o[ ink is difl'i:C"ult because all the components which were originally put int,o the ink by the mnnufnrturer cannot be determined. In


826 some mmsual cases n, posit.h·e identificntion cnn be made when it. NUl be established thu.t n unique dve or combination of component-s was used. For e~nmple, in one particular case, it was possible to est..'l.blish that a doeument dnted 1958 was backdated becttuse a. dye identified in the qurst.ioned ink was not synthesized unt.il 1959. This type of identification can be considered absolute. In another ease, 4 specific ingredients or the ink were identified and it was established that only one ink manufacturer in the lTnited States ~tnd Europe produced an ink with the same combination of ingrt.>dients. The methods described for the analysis of inks are not br any means the only ones that can be used, nor are they !'€presented to be the bl:';;t possible methods. Howl:'ver, these methods arE' belieYed to be tht.> most practictu when considering the sample size. Since each ink is unique, no specific method will apply in all cases. For this reason, the analyst must use the best analytical techniques a\·ailable and determine as many point-s of identification as possiblt.>. The success o£ the described approach to ink identification depends largely 011 the coopemtion of the \"arious ink manufacturers who supply the ink standards. Without their help sufficient standard samples to compare with q ue:stioued ink:; would not be available for this approach to be practical. The Alcohol, Tobacco and Firearms La.boratory has been very fortunate because ink companies have recognized ~he value of this type of program to law-abiding citizens and thus have been extremely cooperative, not only by providing ink samples, but by presenting testimony at court whenever necessary.

Received February 29, 1972.

JounNAL m~ Tim AOAC (Vol. 55, No. 4, 19?2) Fu.tm·e

lnl.~

Cmnpari.sons

The identification of writing inks by the dcscribrd procedm·e cm1 help investigators by providing investigative leads. and the t·esults ob. tnined and conclusions formulated very often nre excellent corroborative evidence in criminal cases. Since the identificn.tion is sta!iistical, this In.boratory is working on a marking pt·ogmm that can be used by all ink manufacturers. The addition or markers, which can be changed yearly, by each producet· cu.n provide a positive identification or the manufnctm·et· of the ink and permit the deter. mination of the year in which the ink was produC'ed. R.EFERENCES

(1) Somerlord, A. W., & Souder, J. L. (!!l52) J. Gr,:m. Law 43, 12•1-127 (2) Brown, C., & Kirk, P. L. (1954) J. Grim. Law 45, 334-3:m (3) Brown, C., & Kirk, P. L. (195<1) J. Crim. Law 45,473-180 (4) Brackett, J. vY., &: Bradford, L. W. (1952) J. Gn:m. Law 43, 53Q-539 (ii) Coldwell, B. B. (1955) rlnalyst 80, ()8-72 (6) Raju, P. S., Banerjee, R. C., & Iyengar, N. K. (1963) J. Ama..:trad. Fomrsic: Sci. 8, 268-285 l7} Feinberg, J. G., &: ~mith, I. (l962) Chromatography and E/atropltorc,;;i8 on Paper, Pergamon

Press, New York (8) Thompson, J. W. (1967) J. Forensic Sci. Soc.1, 194-203 (9) Tholl, J. (1960) Police 7-15 (10) lVIacDonell, H. L. (1962) J. Grim. Law 53, 507521

(11) Crown, D. A., Conway, J. U., & !{ide, P. 1. (1961) J. C1'im. Law 52, 338-343 (12) Nakamura, G. H.., &: Shimada, S. C. (196&) J. Crim. Lmu 56, 113-118 (13) Hamman, B. L. (1968) J. Forens1:c Sci. 13, M4-

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1972_Brunelle R.L., Pro M.J. - A systematic approach to ink identification