GL Newsletter January 2013

Wolf Kuehn, F.G.G., F.G.A., Editor

AGTA GemFair

From the Editor

If you are visiting the Tucson gem shows please drop by at the C.I.G. booth #31 right next to Gem-A at the Galleria Level of the AGTA GemFair from February 5 – 10.

Have a look at the new GL Gem Raman TEC 532PL; the GL Gem Spectrometer will be on display as well. You can read more about new developments in this newsletter.

There will be a special Tucson price for the GL Gem Spectrometer; please go to the on-line store to see more details.

GL Gem Raman Developments

After intensive testing we have finalized the GL Gem Raman PL532 TEC and will introduce this new unit during the Tucson AGTA GemFair.

We modified the Raman spectrometer to increase the range from approx. 75 to 5,400 cm-1 at better than 10 cm-1 FWHM. There is always a trade-off affecting resolution but we were able to stay within the margins required for matching the Raman references in the RRUFF database.

We also expanded the software to allow for photoluminescence studies which may play an important role in identifying possible treatments of diamonds and gems in the future.

Another improvement for the GL Gem Raman was the addition of a thermoelectric cooling (TEC) element. The CCD (3648 pixel CCD Toshiba TCD1304AP linear array) can now be cooled down by – 35 degrees Celsius resulting in up to 150 times lower dark current.

For a gemmological lab doing appraisal work this option is not absolutely necessary as most cut and polished gemstones are fairly good Raman scatterers. However, I encountered several mineral samples which had extremely weak Raman signals and after switching on the TEC (it takes 2 minutes to reduce temperature by -30 C and another 8 minutes to stabilize at – 35 C) I was able to identify the sample. The spectral graphs look much “cleaner” and professional which is important for publication.

The TEC option is recommended for research and can be turned on when required. For up-to-date information go to our special page for the GL Gem Raman.

Nephrite

Extended range of the GL Gem Raman

For gems and minerals the typical Raman fingerprint range is from 145 – 1,500 cm-1 (as in the RRUFF database). The GL Gem Raman PL532 has now an extended range to detect Raman signals up to the 5,400 cm-1 limit (click on image to see more details).

The GLGemRaman program has the option to save both ranges as a [name].rruff file which can be directly loaded into the provided search program.

The Raman spectrum for nephrite above shows features (water band) in the above 1,500 cm-1 range which could not be seen in the previous version of the GL Gem Raman.

The RRUFF project provides for a “broad scan” database with over 1,100 references. However, due to significant increase in search time we recommend to use this database separately from the regular one.

The newest edition of Spekwin32 (revised version 1.71.6.1 from Nov 05 2012, file size: 1.3 MB by F. Menges) will import .rruff files and .fak files from the GL Gem Spectrometer.

Alexandrite Synth PL

PL option for the GL Gem Raman

The GL Gem Raman has a high quality regulated 532nm laser as an excitation source and a proper calibration system to allow scientific research. For PL studies the output of the laser has to be reduced to 50 – 100 mW.

Synthetic and natural alexandrite show the same PL peaks (click on image to see more details).

PL Option: 530 – 750 nm (broad scan) is included for experimental studies (please note that this IS NOT a fluorescence spectrometer).

With the extended range of the GL Gem Raman the PL option is already included. Users can switch the software from a [cm-1] to a [nm] scale which is commonly used for photoluminescence studies. A simple calibration procedure allows for consistent measurements.

Very limited scientific research has been done in this area. This will change in the future as we and others have started conducting studies on diamonds and selected gem materials. However, the GL Gem Raman was designed for Raman and not as a fluorescence spectrometer. We are also working on a laser PL attachment for the GL Gem Spectrometer.

An excellent overview in the interpretation of Raman and PL spectra is given in Jasinevicius, R. (2009) Characterization of vibrational and electronic features in the Raman spectra of gemstones (PDF) (MS thesis, unpublished).

Initial Photoluminescence Studies with the GL Gem Raman

The claim that photoluminescence can be diagnostic for the identification of a gemstone has to be taken with caution – in particular for the detection of HPHT treated diamonds and gemstones. With the PL option now available for the GL Gem Raman I looked at several studies to repeat and verify their testing and results. I have also tested synthetic diamonds of early Russian production in the C.I.G. gem collection.

Some of the results have already been documented in our poster “Raman Spectroscopy – A Powerful Tool in Gem Identification” (PDF, 948 KB). For further information download the GIT 2012 E-Proceedings PDF document from here (over 500 pages, .zip file, 90 MB).

PL reaction of spinel

PL studies to separate synthetic flux grown spinel from natural red spinel

The graph shows (click on image to see more details) the PL main peak for natural red spinel slightly shifted to the left.

The SSEF (Swiss Gemmological Institute) obtained a similar PL reaction using their UV-VIS-NIR spectrometer and a 312 nm LED excitation source as shown in their “Spinel: A Gemstone on the Rise” presentation (PDF)”.

Also read  “Element Analytical and UV-Vis-NIR Study of Natural Untreated Vietnamese and Synthetic Spinels” presented by Tobias Haeger during GIT 2012 (see E-Proceedings, pages 179ff).

Emerald Comparison

PL studies for emerald characterization

Comparing a synthetic flux grown emerald with a natural Colombian emerald one can see a definite shift in the luminescence peaks for chromium (click on image to see more details).

For further information read Le Thi Thu Huong’s thesis “Microscopic, chemical and spectroscopic investigations on emeralds of various origins” (pages 68ff, PDF, 2.2MB).

Origin studies for emeralds have been done based on inclusion characteristics; as a matter of fact the gemmological microscope is still the most important tool to separate natural from man made gemstones. However, with access to advanced instrumentation other approaches will become a possible.

PL Diamond

First PL studies on synthetic diamonds

The unusual PL centre (click on image to see more details) most probably originates not from a point defect in diamond, but from crystalline Al2O3:Cr3+ (ruby) inclusions or impurities in the diamond.

See “Luminescence study of defects in synthetic as-grown and HPHT diamonds compared to natural diamonds” (abstract, last sentence).

GL Gem Spectrometer Developments

The Gl Gem Spectrometer has a user base of over 100 people around the world. Already during the last Tucson gem show several visitors at our booth came up with some new ideas.

P1040540

GL Gem Spectrometer for chromaticity studies

With a firmware modification and extra software module the GL Gem Spectrometer can be used as a colourimeter displaying XYZ colour space coordinates.

For exact measurements an integrating sphere is recommended which mounts right on top of the spectrometer unit.

We are also working on a GLGemSpec laser attachment which would allow PL studies with the GL Gem Spectrometer as a low cost alternative to the GL Gem Raman PL532 unit.

Tucson Specials from the Gemlab Online Store

During January 2013 we will offer the GL Gem Spectrometer to attendants at the Tucson Gem Shows at a reduced price of $ 1,295.00 with free delivery if picked up at our booth # 31 in the Tucson Convention Centre (during the AGTA GemFair from February 5 – 10). More details here.

The GL Xenon Flashlight

This portable Xenon flash-light is ideal for use with the GL Gem Spectrometer as an external light source. Users have experimented with various setups to illuminate samples bigger than can be accomodated in the GL Gem Halogen Holder ; using a fiber probe with the GL Gem Spectrometer requires a customized setup with external lighting and will change several parameters for obtaining a spectrum.

With the Xenon flashlight I was able to clearly resolve the 415 nm line of a Cape series type Ia diamond and produce the typical 437 nm line in green jadeite.

Comparison of emission curves for halogen and xenon light source

GL Gem Spectrometer with the halogen light holder removed

Jadeite, Burma – naturally coloured with typical absorption (edited in Spekwin32)

Read Identification of dyed jadeite (PDF) from The Journal of Gemmology, 2009, 31(5-8). You can buy the GL Xenon Flashlight in our on-line store.

A Mini Microscope for Inclusion Studies

I am a collector of all kinds of gyzmos – amongst them loupes, magnifiers, USB microscopes and lately these small mini-microscopes. I tried quite a few of them and they are becoming better and better.

The best one so far costs less than US$ 5 (please e-mail me for store weblink) and has switchable LED/UV illumination.

Which one is the best?

Which one is the best?

There is a LED/UV switch

There is a LED/UV switch

Inclusions in garnet

Inclusions in garnet

Handbook of Gemmology

The Canadian Institute of Gemmology and Gemlab Research & Technology is a sapphire sponsor of the soon to be published Handbook of Gemmology. Containing over 675 colour photographs, illustrations and diagrams from 130 different contributors in thirty-six countries, ‘The Handbook of Gemmology’ is truly a global project and will be available as an eBook publication through the Gemlab Books & Instruments on-line store  in late February 2013.

GEM 250 GEM IDENTIFICATION II (Advanced Upgrade Course)

Gemmologist

– Course GEM 250-1: Sat – Wed, May 18 – 22, 10 a.m. – 4:30 p.m. (5 days, Richmond, B.C.)

– Fee: $ 995 ($ 200 exam fee for A.G. diploma not included); comprehensive study guide, Gemstone Inclusion Library, use of lab equipment and study stones.

In this course students will learn state-of-the-art techniques including immersionscope, konoscope, gemstone magnetism, IR-VIS-NIR and Raman spectroscopy, etc. designed to identify confidently any gemstone encountered in the industry. Between 100 and 120 challenging gems including the most recent synthetics are available for testing.

Here a brief list of man-made gems in our study collection: Chatham, Kashan, Ramaura, Knischka, Lechleitner, Regency, Biron, Lenix, Gilson, Tairus rubies, sapphires, emeralds, alexandrite, opal, moissanite, CVD and synthetic diamonds and many others. Gem enhancement techniques such as heat-alteration, surface colour diffusion, irradiation, HPHT and glass filling are studied.

Hands-on exercises with our in-house developed GL Gem Spectrometer and GL Gem Raman TEC PL532 system.

Prerequisite: “Gemmologist (C.I.G.)” certificate or similar gemmological qualification. Practicing gemmologists may use this lab class to up-grade their skills. It is also part of the C.I.G. Professional Development Program (AG-PDP).

To Register, please call: 604-530-8569

GEM 370 GL Gem Raman Workshop

This course is for current or future users of the GL Gem Raman system.

ramandesk – Using PowerPoint presentations the development and use of Raman spectrometers is introduced.- Learning step-by-step testing method with GLGemRaman software and searchable database

– Practical testing of a number of interesting gem materials by the participants under supervision of the workshop facilitator.

Presenter: Wolf Kuehn, B.A., M.A., Dipl.oec, FGA, FGG

  • GEM 370-1 Tue, May 21 from 6:30 – 9 p.m. (2 1/2 hours)

Location: Vancouver Airport Hotel TBA, Richmond B.C., Canada

Fee: $ 295 (limited to 5 participants). To register on-line go here.

We reserve the right to cancel courses if there is insufficient enrolment; upon return of all course materials students will receive a full refund for the tuition paid but no other compensation can be offered.

Please wait with travel arrangements until final confirmation.

View/Download and read carefully our refund policy (PDF). View/Download Application Form (PDF) or call: 604-530-8569

Discovering Gems and Jewellery

UBC Continuing Studies at Robson Square is offering as part of their CULTURAL ENRICHMENT program:

ubc – An Introduction (offered in the fall 2013)- For Connoisseurs (offered in the spring 2013)

To register contact UBC Continuing Studies.

WD511W13A Sat, March 2 – April 13, 2013, 12:30-2:30pm; UBC Robson Square. $360+tax

WD510 W13 A Sat, March 2 – April 13, 2013, 3:00 – 5:00pm; UBC Robson Square. $380+tax (Interpreted in Mandarin)