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spectrafromfilmthicknesinbothcases.Inordertocheckwhethertherewassignificantfluorescence present,fluorescencespectrawerexaminedinaPerkinElmerMPF4spectrofluorimeteroverthe completerangeofexcitationfrequenciesandnofluorescencewasobserved.
4. RESULTS
Theinterpretationoftheresultsinageneralsense,isnothelpedbythereticenceofpigmentsupli-
erstodivulgethechemicalnatureoftheirpigments.Thesesupliersevenrefusetoacknowledgethatthey
suplysuchpigments.Giventhelegalimplicationsofanyconditionatributabletothepigmentsthis reticenceisunderstandable.
4.1.IdentityofthePigments
ThepigmentsusedinthecurentstudyweresubjectedtoEnergyDispersiveX-rayFluorescence, EDXRF,analysis(Oxford-TenelecNucleus,Si/Lidetector,170eVresolutionat5.9keV,109Cdsource) andPowderX-raydifractioninordertoacquiresomeknowledgeoftheirchemicalnature.Itisoutofthe questiontoexactlyidentifythesepigments,sincetheyareundoubtedlymixturesandprobablyimpure compounds.Nevertheles,thesestudieswerequiterevealing.TheX-raydifractionconclusivelyproved thatthewhitepigmentwastitaniumdioxideandthatthebluewascoperphthalocyanine.Thegren pigmentsemedtobeamixtureofTi02andacopercompound,butwithahighbrominecontent.
Wededucethatthisprobablyindicatedthepresenceofabrominatedcoperphthalocyanineplus posiblyotherorangepigments.Theyelow,orangeandredpigments,whichpresentsimilarreflectance spectra,arealheavilychlorinatedpigments,theyelowandorangebeingdilutedwithcalciumsulphate. Strangely,thelightredpigmentdoesnotcontainchlorinebutislightenedbyaditionofthexpected Ti02.Infactthereflectancespectra,asusedinthisstudy,provideasimpleandvaluablediagnosticaidto determinewhetherpigmentsamplesareofthesameorigin.Thebrownpigmentwasesentialytwoforms oftitaniumdioxide(anataseandrufle)togetherwithsomeorganicpigment.
4.2.Liquidphasespectra
Giventheinhomogeneousnatureoftheliquidphasespectrainthevisiblewavelengthrange,these
werenotusedasabasisforanydeduction.Theyareshownwiththeacompanyingsolidphasespectra
forcomparison.Inthecaseoftheredpigment(Fig.2)solidphase(1-reflectance)spectrandliquidphase
"absorption"spectrayieldsimilarresults,butinthecaseoftheblueandgrenpigments(Figs.3,5and6)
theliquidphasespectrashowabroadstructurewhichisquitediferentfromthatsenforthesolid.The
scateringpropertiesofthesolidparticlessuspendedintheliquidwilbequitediferentfromthoseofa
filmofsolidparticlesasfoundinatato,sothatsuchdiferencesarenotsurprising.Acordingly,such
spectrareconsideredtobequiteuselesinasesingthebehaviourofthesolidpigmenttolaserradia- tion.
4.3.SolidStateReflectanceSpectra
Thereflectancespectraofthesolidfilmsmaybeclasifiedintotwogroups.Pigmentsthroughthe rangefromredtoyelowandbrownyieldspectrasimilartotheredpigmentasshowninFig.4.Theblue
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