8._Ink_Examination.ppt

Ink examination

1. INKEXAMINATION
Session-8

2. Inksaremadebyincorporatingpigmentsordyes
intoacarriervehicle.Thecarriercontainsmany
othercomponents,addedtocontrolpropertiessuch
asthickness,drying,adhesiontopaper,andflow
fromtheinkreservoir,aswellastheappearanceof
thedriedink.Differentinkmanufacturersuse
differentinkcompositions,butthecolored
componentsofinkcontainonlyafewbasic
substances.

3. Theoldestformofinkisthatmadebysuspending
carbonblackinabindersolution.Theproduct,India
ink,isthemostpermanentofallinks.
Irongallotannateink,composedoftannicacid,
gallicacid,ferroussulfate,andananiline-based
dye,isthebasisformanycommercialwritinginks.
Theanilinedyeproducestheimmediatepigment,
buttheothercomponentsreacttogetherwithtime
toproducethepermanentdye.

4. Mostoftoday’sinksarecomposedofabasicacidic
orneutralorganicdye,derivedmainlyfromcoaltar
orpetroleum.Inksthathavethesamedriedcolorto
thenakedeyecanhavequitedifferentchemical
compositions.
Thecomponentsofdifferentdyeinksvary
sufficientlytoallowcomparisonanddetermination
ofwhetherknownorquestionedwritingswere
preparedwiththesametypeofink.

5. NondestructiveMethodsforInkComparisons
Thereareseveralinstrumentalprocesses
availableforexamininginksinwritten
documents,rangingfromthesimplealternate
lightsourcetocomplexmultifunctiondevices
suchastheFosterandFreemanVSC6000.
Thebasicprinciplesarethesameinmost
cases.SomedyeswillabsorbUVlightand
emitfluorescentlightinthevisibleregionof
thespectrum.

6. Tuningthewavelengthoftheexcitationsourceand
capturingtheemittedlightatvariouswavelengths
increasethevalueofthetechnique.Therelated
techniqueofinfraredluminescenceuseslonger
wavelengths(visibleregion)forexcitation,
whichpushestheemittedlightwavelengthsinto
theinfrared(IR)ranges.UVfluorescenceandIR
luminescencebothdependontheelectronsbeing
raisedtoahigherenergyorbitalbytheirradiated
lightandthenemittinglightofalongerwavelength
whentheydecaytotheirgroundstate.
Fluorescenceandluminescencearevaluabletools
inidentifyingalteredwritingswheredocuments
havebeenchangedusinganinkofthesamevisible
appearancebutdifferentcompositiontoaddtext.

7. Visible Light UV Light IR Light

8. DESTRUCTIVEMETHODSFORINKCOMPARISONS
Thin-layerchromatography(TLC)andhigh-
performanceliquidchromatography(HPLC)arewell-
establishedseparationsciencetechniquesthatcan
beusedtoexploitthemoleculardifferencesofink
components.Thoughdestructivetothesample,they
canhelpacriminalistdeterminewhichdyes,
pigments,orotherchemicalsarepresentinanink
sample.Microdotsofinkcanbepunchedoutofa
writingsampleusingahollowneedle.Alternatively,if
smallamountsoffibercontainingtheinkcanbe
teasedfromthesurface,thesecanbemountedon
theplateasasample.

9. HPLC is the more powerful tool in regards to its
capability to separate dye components, but TLC is
simpler and gives a good visual representation.
Once developed, the TLC plate is examined under
visible and ultraviolet light.

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13. VISUAL SPECTRUM COMPARATOR
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