The beauty of colour © Swiss Gemmological Institute SSEF SGG Zentralkurs, Thun, 15. April 2013 Treatment of corundum characteristics, detection and declaration Michael S. Krzemnicki Swiss Gemmological Institute SSEF Switzerland Photos and figures © H.A. Hänni & M.S. Krzemnicki 1! Consumer+expectation+ Quality& Every&gemstone&deposit&produces&stones&of&high&and&low&quality.& Usually&the&quality&distribution&has&the&shape&of&a&pyramid.&& Top&stones&are&rare,&stones&of&lower&quality&are&very&abundant.& The&exploitation&of&gems&is&expensive,&regardless&of&their&quality.& It&is&economically&and&important&to&be&able&to&enhance&stones&of&& the&lower&part&of&the&quality&pyramid&(also&for&the&miners!)& Once&a&treatment&is&developed&and&successfull,&it&often&is&also&applied&& on&stones&of&better&quality&to&make&them&even&better&looking.& Gem$deposit+production+ Quantity& © SSEF Swiss Gemmological Institute Treatment options for corundum... To&modify&transparency:&& &F&Gilling&of&Gissures&with&colourless&substance&&(oil,&artiGicial&resin,&glass)& &F&heating&to&dissolve&inclusions& & To&modify&colour& &F&Gilling&of&Gissures&with&coloured&substance&(oil,&artiGicial&resin,&glass)& &F&heating&in&oxidising&or&reducing&conditions&(±&with&additives)& &F&diffusion&of&„colouring“&elements&into&the&corundum&lattice& &F&irradiation& & To&enhance&stability& &F&Gilling&of&Gissures/cavities&with&solidifyig&substances&& & To&create&optical&effects&& &F&heating&with&additives& & © SSEF Swiss Gemmological Institute! 2! Treatment options for corundum... Fissure&Gilling&and&dyeing& & Foiling,&Painting& Heating&with&blowFpipe& ©&F.&Notari& Heating&with&electrical&furnace& ©&H.A.&Hänni& Irradiation& Heating&combined&with&surface&diffusion& Heating&with&borax&to&induce&Gissure&„healing“& Beryllium&diffusion& LeadFglass&Gissure&Gilling& & CobaltFglass&Gissure&Gilling& & next&treatment&??& & future& 0& 1000& 1900& 2000& Time+scale+ & © SSEF Swiss Gemmological Institute! Treatment options for corundum... Acceptance&in&the&trade&and&stability& & heating& Heating&with&borax&to& high& induce&Gissure&„healing“& Beryllium&diffusion& CobaltFglass&& Stability+ + Gillings& LeadFglass&& Fissure&Gilling&with&oil&& Gillings& (±&colourless)& irradiation& surface&diffusion& low& & dyeing& low& Acceptance+ high& & + & © SSEF Swiss Gemmological Institute! 3! Talking about treatments... Pailin! © SSEF Swiss Gemmological Institute! Fissure filling with colourless oil: Oiled&Gissures&often&found&in&rubies&or&sapphires&polished&as&beads.&& & SSEF&discloses&oil&in&corundum&only&if&the&amount&in&Gissures&is&moderate& to&signiGicant.& A&Gissure&Gilled&with&oil,& showing&a&characteristic& © H.A. Hänni, SSEF dendritic&pattern.& © SSEF Swiss Gemmological Institute 4! Dyeing/staining with coloured oil: red&dye&in&a&colourless&sapphire&and& in&pinkish&grey&star&corundum.& & On&SSEF&reports,&such&a&dyeing& treatment&is&fully&disclosed!& Photos © H.A. Hänni, SSEF © SSEF Swiss Gemmological Institute Irradiation of corundum: Irradiation&with&high&energy&electromagnetic&radiation& (intense&SWUV,&XFrays,&gammaFrays).& Colourless&or&pale&yellow&stones&become&intensly& brownish&yellow&(amber&colour)&due&to&an&induced& colour&centre.&The&colour&centre&is&however&not+stable+ and&the&colour&will&thus&fade&in&daylight&after&some&time.& Some&natural&untreated&yellow& sapphires&also&show&unstable& colour!&& Photos © H.A. Hänni, SSEF Detection+is+dif;icult.+Usually+these+stones+ are+exposed+to+a+„+fading+test“+under+a+ strong+light+source+(beware+of+heating!).+ 5! Heating of corundum Heating of corundum Colour&in&corundum&is&due&to&the&presence&of&iron&(Fe2+,&Fe3+),&titanium,&magnesium& and&chromium.&Very&important&in&this&respect&are&the&soFcalled&“intervalence&charge& transfer&processes”&with&titanium&Ti4+/Fe2+&and&with&iron&itself&Fe2+/Fe3+.& & &Fe2+/Ti4+ &results&in&blue& & &Fe2+/Fe3+ &results&in&yellow& & Heating&of&corundum&mostly&is&affects&the&valency&of&iron&Fe2+&and&Fe3+&found&as& chemical&impurities&within&the&corundum&lattice.&Secondly&it&may&also&result&in&the& release&of&titanium&Ti4+&into&the&lattice&by&dissolving&rutile&(internal&diffusion)& & Fe2+ & &oxidising&heating & &&Fe3+& & Fe3+ & &reducing&heating & &&Fe2+& & By&this,&many&(but&not&all)&colour&changes&due&to&heating&can&be&explained.& © Swiss Gemmological Institute SSEF 6! Heating of corundum difGicult&to&detect&with&microscope& Low&temperature&heating&(<1000&°C),&e.g.&Mong&Hsu&rubies&and&pink&sapphires& &effect:&colour&shift,&blue&colour&component&is&reduced& & Heating&>&1000&°C,&e.g.&for&geuda&corundum,&rubies&from&Thailand&& Heating &effect:&colour&modiGication,&reducing&visibility&of&inclusions&& & usually&with&characteristic&microscopic&features& & & Heating&with&high&refractive&glass&Glux,&e.g.&lead&glass& &effect:&signiGicant&enhancement&of&transparency&and&colour&(and&stability)& & Heating with flux with Heating&with&borax&Glux,&e.g.&rubies&from&Mong&Hsu&(Burma)& &effect:&signiGicant&enhancement&of&transparency&and&colour&& & Heating&with&chromium&diffusion&(shallow)& &effect:&creation&of&shallow&colour&zone& & Heating&with&beryllium&diffusion&(lattice,&bulk),&e.g.&corundum&from&Songea& Heating &effect:&signiGicant&colour&modiGication& with diffusion with © Swiss Gemmological Institute SSEF Mozambique ruby Heated Heated and fissure filled untreated with an additive (borax) with high refractive glass (lead glass) © Swiss Gemmological Institute SSEF 7! Low Temperature heating (below 1000° C)! Before heating After heating By&the&heating&at&low&temperature&at&oxidising&conditions,&the&blue&colour&component& is&reduced,&thus&a&better&red&to&pink&colour&is&achieved!& © Swiss Gemmological Institute SSEF Detection&of&lowFTemperature&heated&corundum& with&the&microscope&is&very&difGicult& zircon&inclusion&in&& zircon&inclusion&in&& unheated&corundum& heated&corundum& © SSEF Swiss Gemmological Institute 8! Raman&spectra&or&FTIR&spectra&can&be&very&important& for&detection&of&lowFT&heating&of&corundum&!& & heating boehmite&AlO(OH)& FTIR&at&different&Temp.& from Frost et al. 2000 Raman&spectra&of&zircon&inclusions& ©&M.S.&Krzemnicki,&SSEF& heating © Swiss Gemmological Institute SSEF Heating of corundum above 1000° C! At&higher&temperatures,&it&is&possible&to&signiGicantly&enhance&or&modify&the&colour&of& corundum.&Furthermore,&it&is&possible&to&reduce&visibility&of&inclusions.& © Swiss Gemmological Institute SSEF 9! Surface features indicating a heat treatment ! High&temperature&heating&may&produce&„burnmarks“&on&the&surface& ! (but&usually&stones&heated&at&high&temperature&are&reFpolished)& © H.A. Hänni, SSEF © SSEF Swiss Gemmological Institute! Atoll structures Melting&and&explosion&of&inclusions&results&in&characteristic& discoid&features,&the&soFcalled&„atollFstructures“.& © H.A. Hänni, SSEF © H.A. Hänni, SSEF Atoll structures in heated sapphires © SSEF Swiss Gemmological Institute 10! The dissolution of rutile needles © H.A. Hänni, SSEF Rutile+needles+may+partly+dissolve+and+leave+ dust+tracks+in+their+former+place.! Photos © H.A. Hänni, SSEF © SSEF Swiss Gemmological Institute! Partly+dissolved+rutile+results+in+blue+dots+due+to+the+release+ of+titanium+into+the+corundum+lattice+(internal+diffusion)+ © H.A. Hänni, SSEF © SSEF Swiss Gemmological Institute! 11! Heating with high refractive glass flux In&the&last&few&years&large&quantities&of&rubies&heated&at&low+temperatures&with&a& high&refractive&glass&Glux&(e.g.&containing&lead,&bismuth...)&have&entered&the&market.& © H.A. Hänni, SSEF Heated and fissure filled Mozambique ruby with high refractive glass untreated (lead glass) from Andilamena, Madagascar Rutile&needles&may&be&still&present&(sometimes&rubies&show&even&star&effect&!)& © Swiss Gemmological Institute SSEF Blue&and&orange&„Glashes“&& (interferences)&along&leadFglass& Gilled&Gissures.&Also&with&distinct& Glattened&air&bubbles&along&Gissures.&& At&these&low&temperatures,&no& „healing“&of&Gissures&occurs!& © H.A. Hänni, SSEF Detection+easy+with+the+microscope!+ © Swiss Gemmological Institute SSEF 12! SEM&BSE&micrograph:& Fissures&Gilled&with&PbF glass&are&bright.& Pb$glass+;illed+ruby+is+easy+to+ detect+with+chemical+analysis,+ XFray&microtomography& radiography+and+ of&PbFglass&Gilled&ruby.& X$ray+microtomography+ © Swiss Gemmological Institute SSEF New: Heating with Co-bearing flux Photos & spectra© T. Leelawatanasuk & O. Papawarin, GIT! Colourless&corundum&with&distinct&CoF blue&Gissure&Gillings&(and&distinct&Co& spectra&!)& Easy+to+detect+with+microscope+!+ © Swiss Gemmological Institute SSEF 13! Heating with a Flux (Borax: Na-B-Hydroxide): Microscopic Evidences Flux&residues&in&tentacleFlike&irregular&pattern&in&a&ruby&from&Thailand&(Siam)&heated& with&a&borax&Glux.& Photos © H.A. Hänni, SSEF Attention:+ polycrystalline+;lux+ in+;lux$melt+ synthetic+ruby+!+ Residues&of&Glux&(glass)&in&thin&Gilms,&curved&tubes&and&networks,&forming&& a&soFcalled&„neoFhealing&Gissure.& © SSEF Swiss Gemmological Institute 14! Version 4. December 2011 Information Sheet #1 Standardised Gemmological Report Wording (To be approved by 15 January 2012) Corundum • with residues from the heating process present in healed fissures • with residues from the heating process present in filled cavities Members of the Laboratory Manual Harmonisation Committee (LMHC) have standardised the nomenclature that they use to describe heat treatment in corundum and the degree to which fissure “healing” has occurred, and the residues that remain within the healed fissures and cavities, following the heating of corundum. Healed fissures1: Any corundum