SGG Corundum treatment - ssef.ch · 6! Heating of corundum...
Transcript of SGG Corundum treatment - ssef.ch · 6! Heating of corundum...
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,®ardless&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!
Treatment options for corundum...
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&
Treatment options for corundum...
Acceptance&in&the&trade&and&stability&
© SSEF Swiss Gemmological Institute!
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!
© SSEF Swiss Gemmological Institute!
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.&
© SSEF Swiss Gemmological Institute
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:
© SSEF Swiss Gemmological Institute
Photos © H.A. Hänni, SSEF
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¢re.&The&colour¢re&is&however¬+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¬&all)&colour&changes&due&to&heating&can&be&explained.&
Heating of corundum
© Swiss Gemmological Institute SSEF
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
© Swiss Gemmological Institute SSEF
Hea
ting
Hea
ting
with
flux
H
eatin
g w
ith d
iffus
ion
difGicult&to&detect&withµscope&
usually&with&characteristicµscopic&features&
Mozambique ruby untreated
Heated with an additive (borax)
Heated and fissure filled with high refractive glass
(lead glass)
© Swiss Gemmological Institute SSEF
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
© Swiss Gemmological Institute SSEF
© SSEF Swiss Gemmological Institute
zircon&inclusion&in&&unheated&corundum&
zircon&inclusion&in&&heated&corundum&
Detection&of&lowFTemperature&heated&corundum&with&theµscope&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
© Swiss Gemmological Institute SSEF
Raman&spectra&or&FTIR&spectra&can&be&very&important&for&detection&of&lowFT&heating&of&corundum&!&
© 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.&
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)&
© SSEF Swiss Gemmological Institute!
© H.A. Hänni, SSEF
Atoll structures
© SSEF Swiss Gemmological Institute
Melting&and&explosion&of&inclusions&results&in&characteristic&discoid&features,&the&soFcalled&„atollFstructures“.&
Atoll structures in heated sapphires
© H.A. Hänni, SSEF
© H.A. Hänni, SSEF
11!
The dissolution of rutile needles
© SSEF Swiss Gemmological Institute!
© H.A. Hänni, SSEF
Photos © H.A. Hänni, SSEF
Rutile+needles+may+partly+dissolve+and+leave+dust+tracks+in+their+former+place.!
© SSEF Swiss Gemmological Institute!
© H.A. Hänni, SSEF
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
© Swiss Gemmological Institute SSEF
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
© H.A. Hänni, SSEF
© 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!&
Detection+easy+with+the+microscope!+
© H.A. Hänni, SSEF
13!
© Swiss Gemmological Institute SSEF
SEM&BSEµgraph:&Fissures&Gilled&with&PbFglass&are&bright.&
Pb$glass+;illed+ruby+is+easy+to+detect+with+chemical+analysis,+radiography+and+X$ray+microtomography+
XFrayµtomography&of&PbFglass&Gilled&ruby.&
© Swiss Gemmological Institute SSEF
Easy+to+detect+with+microscope+!+
Colourless&corundum&with&distinct&CoFblue&Gissure&Gillings&(and&distinct&Co&
spectra&!)&
New: Heating with Co-bearing flux
Photos & spectra© T. Leelawatanasuk & O. Papawarin, GIT!
14!
Flux&residues&in&tentacleFlike&irregular&pattern&in&a&ruby&from&Thailand&(Siam)&heated&with&a&borax&Glux.&
Heating with a Flux (Borax: Na-B-Hydroxide): Microscopic Evidences
© SSEF Swiss Gemmological Institute
Residues&of&Glux&(glass)&in&thin&Gilms,&curved&tubes&and&networks,&forming&&a&soFcalled&„neoFhealing�&Gissure.&
Photos © H.A. Hänni, SSEF
Attention:+polycrystalline+;lux+
in+;lux$melt+synthetic+ruby+!+
15!
Quantification of flux residues
© Swiss Gemmological Institute SSEF
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)
© Swiss Gemmological Institute SSEF
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!
© SSEF Swiss Gemmological Institute!
© H.A. Hänni, SSEF
© R. Hughes
Heating with beryllium diffusion (lattice, bulk)
© Swiss Gemmological Institute SSEF
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&isµscopically&very&difGicult&to&detect,&as&an&eventual&orange&rim&is&often&very&difGicult&to&see.&The&colour&is&usually&stable&even&after&a&repolish&!&
Photos © H.A. Hänni, SSEF
17!
Detection of heating with beryllium diffusion
© Swiss Gemmological Institute SSEF
Difficult with the microscope! Photos © H.A. Hänni, SSEF
Detection of heating with beryllium diffusion
© Swiss Gemmological Institute SSEF
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
© SSEF Swiss Gemmological Institute
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
© Swiss Gemmological Institute SSEF
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&!&