SGG Corundum treatment - ssef.ch · 6! 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

1!

© Swiss Gemmological Institute SSEF

The beauty of colour

Michael S. Krzemnicki

Swiss Gemmological Institute SSEF Switzerland

Photos and figures

© H.A. Hänni & M.S. Krzemnicki

Treatment of corundum

characteristics, detection and declaration

SGG Zentralkurs, Thun, 15. April 2013

2!

Gem$deposit+production+

Consumer+expectation+

© SSEF Swiss Gemmological Institute

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.&

Quality&

Quantity&

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!

3!


Time+scale+& © SSEF Swiss Gemmological Institute!

Fissure&Gilling&and&dyeing&&

Heating&with&blowFpipe&

Heating&with&electrical&furnace&

Irradiation&Heating&combined&with&surface&diffusion&

Beryllium&diffusion&LeadFglass&Gissure&Gilling&& CobaltFglass&Gissure&Gilling&

&

Heating&with&borax&to&induce&Gissure&„healing“&

next&treatment&??&&

1000& 1900& 2000&

Foiling,&Painting&

0&

future&

©&F.&Notari&

©&H.A.&Hänni&


Acceptance&in&the&trade&and&stability&


Fissure&Gilling&with&oil&&(±&colourless)&

heating&

irradiation&surface&diffusion&

Beryllium&diffusion&

LeadFglass&&Gillings&

CobaltFglass&&Gillings&

Heating&with&borax&to&induce&Gissure&„healing“&

Acceptance++

low&&

high&&

Stability+

+low&

&

high& &

dyeing&

4!

Pailin!


Talking about treatments...

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&dendritic&pattern.&© H.A. Hänni, SSEF

5!

Photos © H.A. Hänni, SSEF

red&dye&in&a&colourless&sapphire&and&in&pinkish&grey&star&corundum.&&On&SSEF&reports,&such&a&dyeing&treatment&is&fully&disclosed!&

Dyeing/staining with coloured oil:



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.&

Detection+is+dif;icult.+Usually+these+stones+are+exposed+to+a+„+fading+test“+under+a+strong+light+source+(beware+of+heating!).+

Some&natural&untreated&yellow&sapphires&also&show&unstable&colour!&&

6!

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.&

Heating of corundum


7!

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&&&effect:&colour&modiGication,&reducing&visibility&of&inclusions&&

&&&Heating&with&high&refractive&glass&Glux,&e.g.&lead&glass&

&effect:&signiGicant&enhancement&of&transparency&and&colour&(and&stability)&&

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&&effect:&signiGicant&colour&modiGication&

Heating of corundum


Hea

ting

Hea

ting

with

flux

H

eatin

g w

ith d

iffus

ion

difGicult&to&detect&with&microscope&

usually&with&characteristic&microscopic&features&

Mozambique ruby untreated

Heated with an additive (borax)

Heated and fissure filled with high refractive glass

(lead glass)


8!

Low Temperature heating (below 1000° C)!

By&the&heating&at&low&temperature&at&oxidising&conditions,&the&blue&colour&component&is&reduced,&thus&a&better&red&to&pink&colour&is&achieved!&

Before heating

After heating



zircon&inclusion&in&&unheated&corundum&

zircon&inclusion&in&&heated&corundum&

Detection&of&lowFTemperature&heated&corundum&with&the&microscope&is&very&difGicult&

9!

heating

heating

Raman&spectra&of&zircon&inclusions&©&M.S.&Krzemnicki,&SSEF&

&boehmite&AlO(OH)&

FTIR&at&different&Temp.&from Frost et al. 2000


Raman&spectra&or&FTIR&spectra&can&be&very&important&for&detection&of&lowFT&heating&of&corundum&!&


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.&

10!

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

Atoll structures


Melting&and&explosion&of&inclusions&results&in&characteristic&discoid&features,&the&soFcalled&„atollFstructures“.&

Atoll structures in heated sapphires



11!

The dissolution of rutile needles




Rutile+needles+may+partly+dissolve+and+leave+dust+tracks+in+their+former+place.!



Partly+dissolved+rutile+results+in+blue+dots+due+to+the+release+of+titanium+into+the+corundum+lattice+(internal+diffusion)+

12!

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.&

Heated and fissure filled with high refractive glass

(lead glass) Mozambique ruby

untreated

Rutile&needles&may&be&still&present&(sometimes&rubies&show&even&star&effect&!)&

from Andilamena, Madagascar



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!&

Detection+easy+with+the+microscope!+


13!


SEM&BSE&micrograph:&Fissures&Gilled&with&PbFglass&are&bright.&

Pb$glass+;illed+ruby+is+easy+to+detect+with+chemical+analysis,+radiography+and+X$ray+microtomography+

XFray&microtomography&of&PbFglass&Gilled&ruby.&


Easy+to+detect+with+microscope+!+

Colourless&corundum&with&distinct&CoFblue&Gissure&Gillings&(and&distinct&Co&

spectra&!)&

New: Heating with Co-bearing flux

Photos & spectra© T. Leelawatanasuk & O. Papawarin, GIT!

14!

Flux&residues&in&tentacleFlike&irregular&pattern&in&a&ruby&from&Thailand&(Siam)&heated&with&a&borax&Glux.&

Heating with a Flux (Borax: Na-B-Hydroxide): Microscopic Evidences


Residues&of&Glux&(glass)&in&thin&Gilms,&curved&tubes&and&networks,&forming&&a&soFcalled&„neoFhealing�&Gissure.&


Attention:+polycrystalline+;lux+

in+;lux$melt+synthetic+ruby+!+

15!

Quantification of flux residues


minor& moderate& signiGicant&

See&also&LMHC&Infosheet&1:&www.lmhcFgemology.org&

Version 4. December 2011

Page 1 of 2

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 that shows indications of having undergone heat treatment and a degree of healing along (previous) fractures - see Figure 1 - which also contain a residue(s) from the heating process, shall be described as « species » ‘(natural)2 corundum’, « variety » ‘ruby or sapphire’ « further information » ‘indications of heating’ (to modify the colour and/or transparency of the stone), plus the appropriate residue quantification terminology – alpha numeric and/or text description3. See table 1 and examples in figures 2, 3 and 4. Note 1: As an option, e.g., for “simplified reporting” situations, the quantification of residues in healed fissures may be replaced by the statement ‘residues in healed fissures’. Note 2: Wording in parenthesis is optional. Note 3: This clause may include the presence of small filled cavities.

a

b

Figure 1: Flux assisted healing of a fracture during the heating process. A fracture that has been healed by the synthesis of Corundum or other materials during the heat treatment or crystal growth processes. (Hänni, H.A., 1998) (a) schematic (b) actual

Table 1: Residue quantification terminology Condition → No indications

of heating Indications of heating (no residue)

Indications of heating with residues in fissures

Report Alpha numeric →

NTE TE TE1 TE2 TE3 TE4 TE5

Report Text →

No indications of heating

Indications of heating

Minor residue in fissures Moderate residue in fissures

Significant residue in fissures

Condition → Indications of heating with residues in cavities Report Alpha

numeric→ C1 C2 C3

Report Text→

Minor Moderate Significant Residue in cavities Residue in cavities Residue in

cavities

1 (see Information Sheet #3 for "corundum with glass filled fissures" and subsequent "corundum with/and glass") 2 Wording in parenthesis is optional. 3 In the cases of TE1 and TE2 (minor) or TE3 and TE4 (moderate), when the text version is selected a reference to the specific alpha-numeric shall be indicated either by combining the two or placing an « x » in the appropriate point of the comparative scale.

Heating with surface diffusion (shallow)


A&colouring&element&(titanium&or&chromium)&from&an&external&source&is&entering&the&corundum&lattice&during&a&prolonged&heat&treatment&at&high&temperature.&The&result&is&a&very&shallow&intensly&coloured&zone&at&the&surface.&The&colour&is&easily&lost&after&repolishing.&

Cr-diffusion treated Untreated (or heated)

Detection+with+the+microscope+and+chemically+

Photo © H.A. Hänni, SSEF

16!

!!

Comparison&of&a&diffusion&treated&sapphire&(left)&with&a&natural&sapphire&(right)&in&immersion.&The&facet&edges&and&the&girdle&of&the&diffusion&treated&stone&show&

characteristic&colour&concentrations.&

surface diffusion! natural!



© R. Hughes

Heating with beryllium diffusion (lattice, bulk)


Beryllium diffusion treated rubies from Songea (Tanzania)

Beryllium&from&an&external&source&is&deeply&penetrating&the&corundum&lattice&during&a&prolonged&heat&treatment&at&high&temperature.&The&result&is&usually&a&signiGicant&colour&modiGication.&This&treatment&is&microscopically&very&difGicult&to&detect,&as&an&eventual&orange&rim&is&often&very&difGicult&to&see.&The&colour&is&usually&stable&even&after&a&repolish&!&


17!

Detection of heating with beryllium diffusion


Difficult with the microscope! Photos © H.A. Hänni, SSEF

Detection of heating with beryllium diffusion


Safe detection only with LIBS, LA-ICP-MS and SIMS

LIBS&spectra&of&beryllium&diffusion&treated&orange&sapphire.&The&high&beryllium&peak&is&measured&in&the&glassy&residue&at&the&surface!&The&corundum&shows&smaller&peaks,&indicating&approx.&30&ppm&Be&(low&traces!),&but&which&is&already&enough&for&a&colour&modiGication.&

Be

Al

Al

Al

18!

Multi-step Treatments: Creating a star effect


Beryllium&diffusion&treatment&followed&by&titanium&diffusion&treatment&&and&subsequent&annealing&results&in&a&precipitation&of&tiny&oriented&rutile&needles&

creating&a&surfaceFrelated&star&effect&(asterism).&

Disclosure


The&Swiss&Gemmological&Institute&SSEF&uses&a&full&disclosure&policy&following&CIBJO&and&LMHC&(Laboratory&Manual&Harmonization&Committee&with&the&members&CISGEM,&GAAJ,&GIA,&Gübelin&GGL,&GIT,&SSEF)&recommendations:&&Unheated&ruby: &F&No&indications&of&heating&&

Heated&ruby: &F&Indications&of&heating&&

Heated&with&Glux: &F&Lead&glass&Gilled&Gissures&and&cavities&&&& &&&&Extent:&signiGicant&(minor,&moderate)&&&& &&&&The&introduction&of&lead&glass&into&Gissures&involves&heating&&&& &&&&This&treatment&usually&applies&on&low&quality&stones.&

&

& &F&Indications&of&heating&with&minor/moderate/signiGicant&&&&& &&&&residues&in&healed&Gissures&

&

Heating&with&diffusion:&F&Indications&of&heating&&&& &&&&Colour&modiGied&by&shallow/lattice&diffusion&of&titanium/&& &&&&chromium/&beryllium&from&an&external&source&

Internationally&harmonized&wording&for&the&conGidence&of&the&customers&!&

19!

Thank you for your attention


Documents

SGG Corundum treatment - ssef.ch · 6! 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