GL Newsletter April 2012

From the Editor

We had many (and several American friends from WA state) visiting our booth at the BC Gem & Mineral Show last week-end. Every day the GL Gem Raman attracted mineral collectors who tested their samples and made suggestions about how the Raman could be modified for their particular applications (at additional cost); we will be looking into it as some of the features might be of interest to gemmologists as well.

We have started preparing for the Geo-Raman in Nancy, France (June 11-13); I am looking forward to meeting several colleagues and demonstrating the GL Gem Raman . We also added two new refractometers to our gem testing tools in the online store.

New Refractometers

The new compact and fairly accurate GL Gem Refractometer (on-line price $ 129.95) is a good choice for the beginner gemmologist and non-professional user. Like all basic Chinese refractometers the units had to be manually recalibrated against our R.I. 1.4703 reference stone.

Very impressive is the performance of the new and redesigned GL Professional Refractometer (on-line price $ 349.95); it comes in a white plastic casing and was actually properly calibrated.

The refractometer has a high hardness CZ (cubic zirconia) hemicylinder and a built in LED-based yellow light source that is powered by either two AA batteries or a small 110-240V power supply with 3VDC output.

The scale is very easy to read and the shadow lines are very sharp; the refractometer is more accurate than the Japanese built Kyowas we purchased for the C.I.G. classes some 20 years ago for $ 650 each.

This new professional refractometer has the best performance for its price and is highly recommended.

GL Gem Raman Upgraded

Before delivering the first production units of the GL Gem Raman we were able to change slightly the design of the optical path and replace one lens. As a consequence the Raman signal has improved by 20 – 30% eliminating the second step required for readjusting exposure before subtracting the background.

After focusing the Raman beam the default exposure is now sufficient to get an excellent Raman spectrum off most surfaces. In this sense the Raman is easier to operate than the GL Gem Spectrometer and faster to obtain results. Watch “How to obtain a spectrum with the GL Gem Raman” – (video, no sound – window will pop up) of green untreated jadeite.

All Ramans delivered have already the modified design and the units are slightly smaller and lighter than the proto-type. For up-to-date information go to our special page for the GL Gem Raman.

GLGemSpec News

We have updated the on-line version of “How to Get Started” instructions (for registered GLGemSpec users; can be translated). For additional spectral information we recommend the Edward J. Gübelin Collection which contains unpolarized spectra of a wide variety of gemstones in the 350-750 nm range.

For testing opaque materials or gemstones with little or no light transmission such as diamonds an additional light source (fiber optics halogen light or Xenon flash-light) should be used.

We now carry a good quality portable Xenon flashlight in the on-line store.

We compared the radiation spectrum of the built-in GL Halogen 10W Gem Holder and the Xenon flashlight. To reduce noise in the near UV region we are running the 10W/12V halogen bulb hotter at 15Volts.

The Xenon light can be used with the GL Gem Holder or unmounted as an excternal light source.

The Xenon light ( 7.4V 15W bulb) comes with 2x CR123A Lithium 3V batteries; however, we recommend to use rechargeable batteries of type 16340. These batteries are rated 4.2V at full charge each and will produce an illuminance of 154.00 lux overall with an output of 214.06 lumens (according to the manufacturer) which is quite impressive.

Searchable Database for the GL Gem Spectrometer

We have been looking for a spectral recognition software/database program for some time; unfortunately commercial programs cost from $ 1,000 – 2000 exceeding the cost of the spectrometer. Analysis of transmission spectra is complex as it is much dependent on optical path which will affect the appearance of the spectrum.

Search

Thermo Scientific provides a Spectra ONLINE service which can be used with GLGemSpec files. We have tried it and it may be useful for the identification of certain samples.

First the GLGemSpec file *.fak has to be imported into Spekwin 32 and saved as a *.spc (THERMO Galactic GRAMS) file. If your spectrum has not been normalized in the GLGemSpec program it can be done here before saving.

On the on-line data entry browse to your saved *.spc file and submit it. A new window appears: under “Technique” select UV-VIS Spectrum, under “YUnit” Absorbance or Transmission, leave the “Algorithm” in the default option with “Auto-Baseline” ON. Then click “Search”.

The results show references with similar spectra and their chemical composition.

Geo-Raman Xthmeeting, Nancy (France) from June 11 – 13, 2012

“Geo-Raman meetings started in Paris in 1986 followed by Toulouse (1989) and Nantes (1996). The meeting moved out of France for the first time in 1999 (Valladolid-Spain) and continued a wide international journey, Prague 2002, Hawaii 2004, Granada 2006, Gent 2008 and Sydney 2010. They are focused on the application of Raman Spectroscopy to Earth Sciences from the surface to the deep mantle and to earth materials used in cultural heritage. Such meetings are typically interdisciplinary and allow Earth scientists and Raman spectroscopists to present their latest results obtained in these disciplines and discuss transversally. Raman instrumentation and in situ experimentation are also a part of such meetings since this optical spectroscopy in a huge variety of environment including the exploration of planet of the solar system”. For more information visit the website.

We submitted an abstract (320KB, PDF) and a poster (950KB, PDF) “The GL Gem Raman – a poweful tool in gem and mineral identification”  and will demonstrate the GL Gem Raman during the conference. Please contact me if you are interested in attending.

New Studies on Tibetian Andesine

In the never ending story of Andesine several articles have been published recently which are of interest:.

Joel Arem’s (PhD, F.G.A.) article Observations on the Occurrence of Plagioclase Feldspars (PDF) was also published in the ICA’s (International Colored Gemstones Association) magazine InColor – Winter ’11 (Electronic version)

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Wolf Kuehn, B.A., M.A., Dipl.oec, F.G.A., F.G.G. – GLR&T Project Manager