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 Post subject: IIa HPHT treated diamonds
PostPosted: Thu Jun 09, 2011 11:16 am 
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Many gemologists are aware about the IIa HPHT treated diamond issue and how difficult is to be sure about spotting the treatment , there are of course some diagnostic features that can help in dropping a seasoned guess (graphytized surfaces/included crystals, frosted naturals/girdle facets, tatami effects at crossed polars et al.....) but, IMHO there’s no smoking gun available without the help of advanced techniques (well, maybe a graphytized surface could be interpreted as an "almost smoking gun”).
my question is: does the PL spectrometry provide for the only proved evidence of the treatment?
Or turning the question: does the treatment can be certainly spotted with other (advanced) techniques than the PL spectrometry?
Thank you in advance for any wise (or not) input….
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alberto

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 Post subject: Re: IIa HPHT treated diamonds
PostPosted: Sun Jun 26, 2011 1:07 pm 
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It is my understanding that it is a tough call without sophisticated spectroscopic instrumentation.
I stumbled on a relevant article:
Diamond Color Treatments and Identification
by Sharon Ferber, DG GC
[pdfview]http://www.gci-gem.com/pdf/diamond%20color%20treatments%20and%20identification.pdf[/pdfview]

Determining if the diamond was a Type IIA would be the first step.
Some time ago, Jean-Marie Arlabosse explained how to inexpensively rig up a gizmo to check whether or not a gem was transparent to short wave ultra-violet light.


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 Post subject: Re: IIa HPHT treated diamonds
PostPosted: Sun Jun 26, 2011 1:48 pm 
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some tips from Gems & Gemology:
Quote:
The hand or desk-model spectroscope shows a spectrum that is characteristic for most HPHT diamonds: a strong band at about 480–500 nm, a strong line at 503 nm, and sometimes a weak line at 415 nm and/or emission lines at 505 and 515 nm.


Quote:
indication of HPHT treatment:
a strong line at 503 nm, a dark band from about 480 to 500 nm, and green emission lines at 505 and 515 nm visible in the spectroscope.


i guess you have digital spectroscope, so you can test it

Quote:
Photoluminescence. The photoluminescence (PL):
technique measures the intensity of light emitted from a sample, as a function of wavelength, in response to excitation by UV radiation or visible light. In general, different wavelengths of excitation will produce different PL spectra. Laser Raman microspectrometry, a standard analytical technique in many gemological laboratories, is a special case of PL spectroscopy where the emitted light of interest is produced by characteristic vibrations of molecules and crystals. In this study, however, fluorescence
was the emitted light of interest.




anyway with advanced instruments like UV–Vis–NIR and IR Absorption Labs also can do tests but the infrared test is good for lower color grades (after I)

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 Post subject: Re: IIa HPHT treated diamonds
PostPosted: Sun Jun 26, 2011 1:56 pm 
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thank you to both of you.

it's my understanding that no one of the features/techniques posted above can be considered as a "smoking gun", indications of probability, at best.
for what i know the Raman PL spectroscopy at low T° is the most reliable test nowadays, neverthless it's still under ongoing studies......
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alberto

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 Post subject: Re: IIa HPHT treated diamonds
PostPosted: Sun Jun 26, 2011 2:04 pm 
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you are welcome Alberto,
and you are right about Raman, it is most definite test although its very expensive, but there are cheap instruments like HRD D-Screen (but not definite) that trade and small lab can use ;)

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 Post subject: Re: IIa HPHT treated diamonds
PostPosted: Sun Jun 26, 2011 2:06 pm 
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Further research has been conducted in Treated Diamond Identification:
Dr. Mark Newton
University of Warwick, United Kingdom
Dr. Newton leads a physics team in studying color centers in natural, synthetic and treated diamonds.

Dr. Wuyi Wang, Director of Research and Development, GIA, New York, USA
Dr. Wang has spent the last 20 years devoted to diamond geochemistry with an emphasis on treatment.

Analysis of HPHT-Treated Diamonds Using Fluorescence Observations
by Sally Eaton-Magaña and Karen Chadwick, GIA Laboratory, Carlsbad

Just as a relevant sidebar, here is an excellent article on the importance of
Type Classification of Diamonds
by Christopher M. Breeding and James E. Shigley
[pdfview]http://www.shoregold.com/_resources/The-Type-Classification-System-of-Diamonds_C_Breeding_J_Shigley.pdf[/pdfview]


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 Post subject: Re: IIa HPHT treated diamonds
PostPosted: Sun Jun 26, 2011 2:09 pm 
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roshanravan wrote:
, but there are cheap instruments like HRD D-Screen (but not definite) that trade and small lab can use ;)


those tools can give you only a clue about separating IIA type diamond from the other types via SWUV transparence.
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alberto

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 Post subject: Re: IIa HPHT treated diamonds
PostPosted: Sun Jun 26, 2011 2:13 pm 
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Thank you Barbra,

Barbra Voltaire wrote:
Just as a relevant sidebar, here is an excellent article on the importance of
Type Classification of Diamonds
by Christopher M. Breeding and James E. Shigley


that is exactly the article which was the core of Christopher Breeding lecture at the CIGES 2011 in Bari, very very nice lecture...

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alberto

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 Post subject: Re: IIa HPHT treated diamonds
PostPosted: Sun Jun 26, 2011 2:54 pm 
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The discovery by EGL, USA, of the first visual observational criteria for identifying high-pressure, high-temperature treated (HPHT) diamonds, which they termed the "fluorescence cage," ( a specific luminous, intersecting pattern along the cut edges and vertices of facets on particular colored HPHT-treated diamonds with less than strong fluorescence) is described in the article above by Sally Eaton-Magaña and Karen Chadwick.

This is what Alberto is referring to as the "tatami effect".


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 Post subject: Re: IIa HPHT treated diamonds
PostPosted: Sun Jun 26, 2011 3:42 pm 
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Barbra Voltaire wrote:
The discovery by EGL, USA, of the first visual observational criteria for identifying high-pressure, high-temperature treated (HPHT) diamonds, which they termed the "fluorescence cage," ( a specific luminous, intersecting pattern along the cut edges and vertices of facets on particular colored HPHT-treated diamonds with less than strong fluorescence) is described in the article above by Sally Eaton-Magaña and Karen Chadwick.

This is what Alberto is referring to as the "tatami effect".


the fluorescent cage is what you can see in the gemlab equipment webpage (scroll down till Tunable Luminescence Imaging System with Microscope, Cooled Camera and Cooled High resolution High Sensitivity Spectrometer), the article you posted above (Analysis of HPHT-Treated Diamonds Using Fluorescence Observations) is related to type I hpht treated stones, not IIa.
The tatami effect is the crossed strain visible at crossed polars in many treated stones (here an old related article
), unfortunately heavy strain is typical of IIa untreated diamonds aswell, i shot some nice pictures of a D VVS1 9 ct IIa stone but i don't have'em here at home, tomorrow i'll post'em.

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alberto

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 Post subject: Re: IIa HPHT treated diamonds
PostPosted: Mon Jun 27, 2011 3:35 am 
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here a shot of the phenomenon

Image

ciao
albé

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