The Academy of Valuers
Report. Common Gem Treatments Theory and Practical Class Wednesday 26th April 2017.
Presented by Dr Çiğdem Lüle. PhD, FGA, GG (GIA), DGA
Heat, Diffusion and Sintered Cavities etc.
I was so pleased to see the announcement for a practical workshop opportunity which arose in March this year and I jumped at the chance to attend a workshop which offered an opportunity to learn and handle samples of treated gemstones.
Shirley Mitchell greeted a group of fifteen keen and eager valuers on an early spring day in Hatton Garden for the inaugural workshop arranged by the Academy of Valuers. We were introduced to Dr. Çiğdem Lüle and settled down to an intriguing PowerPoint presentation which began with the history of gemstone treatments. This surprised most of us in the room when we learned that gemstone treatments have been used since Roman times and before. Crackled and dyed quartz being one of the most common, many of us remembered seeing examples of these in The Cheapside Hoard Exhibition.
Çiğdem explained the importance of a valuer being able to identify the common gemstone treatments used today and in the past, a challenge which has beset the jewellery industry for years and of course always affects the cost prices and values. Çiğdem mentioned an important distinction which is worth remembering, Gem Treatment is a process Gemstone Enhancement is the result of the treatment. We were told the only way to identify and evaluate treatments begins as always with a jeweller’s loupe but the use of a microscope is essential.
The presentation continued by highlighting the various treatments which included, Heat, Clarity enhancements, Diffusion, Dying/Bleaching, Irradiation, Coatings and Composites. We were all aware of these basic treatments, however Çiğdem explained the intricacies of how the techniques were being implemented. A surprise came when we learned that most wholesalers or gemstone dealers are usually unaware of how the treatments are done in practice and to what extent, they usually just state that a gemstone is ‘treated’, sometimes with general caveats that they are, heated, irradiated, dyed etc. etc. Quite often the heat treatment processes used by the various miners/suppliers/labs are a closely guarded secret and the commercial jewellery trade are kept purposely in the dark about the techniques involved. Another revelation revealed was that globally new treated gemstones enter the market before the treatment process is disclosed. However, identifying the new types of treatments used can only be established by updating ones knowledge gained from this type of workshop or by submission to a Gem Laboratory.
The sticky subject of nomenclature was mentioned, which is so important USA law and has yet, if ever, to become a major legislation issue in the UK. History suggests that we as valuers will have to keep up to date with any future legislation which may require us to disclose as much detail as required when appraising treated gemstones. Obviously, when armed with the necessary knowledge we can include all the information required to make our appraisals complete and as professional possible.
We learned how heat treatments (and some low or high pressure treatments) affect gemstones and usually changes the structure of them permanently. However not all gemstones can be successfully heat treated. Interestingly in corundum, Çiğdem explained how rutile inclusions are changed at various temperature ranges and to how to gauge the approximate temperatures used.
Clarity enhancements have been known since antiquity and Çiğdem explained that any gemstone with surface reaching breaks have the potential for clarity enhancement. The microscope and the ‘flash effect’, being the main method of detection. We found the practical session later to be most useful as there was an array of various fractured filled gemstones and laser drilled diamonds, (including the notorious red glass filled ruby composite imitation), and oiled emeralds which we could handle and view under magnification. Remembering this type of treatment changes the appearance of real gemstones but not the structure.
We learned how some by not all diffusion treatments also leave tell-tale signs in corundum one of which includes surprising, Sintered Cavities when titanium oxide is used. Intriguingly the titanium treatment is done after faceting and then re-polished but can leave tiny heated sintered cavities behind produced by the very high temperatures used. We were able to see these unusual marks for ourselves later using a microscope which was most satisfying. Then Beryllium surface diffusion was discussed which is undetectable as opposed to the colouring agents of Titanium diffusion, which usually leave surface indications on the facet edges etc.
Irradiation treatments used for colour enhancement are impossible to detect without the use of expensive advanced spectroscopy equipment. We were left wondering (jokingly), whether we may need to include a Giger Counter in our collection of gem testing instruments sometime in the future, as this process is often worryingly unregulated in many countries. Irradiation is not always permanent and various techniques are used to stabilise the colour change by heating and annealing the stones afterwards. There are some species of gemstones which should be assumed to be irradiated such as blue topaz and most fancy coloured diamonds amongst others. Notwithstanding a Diamond Report may be required to ensure certainty.
Coatings, Dyed and Composites gemstones provided a welcome break as we all realised they can appear to be very comical with a range of garish colours and textures. During the practical session we handled various types of these gemstones, including many types of pearls in various unnatural colour ranges. We learned the use of diffused lighting on the microscope and how a dichroscope is required to aid detection. Coated stones can often cause the Pleochroism to disappear altogether, especially with Zoisite/Tanzanite. However, not to be become too complacent as some coatings can be very difficult to detect, especially with diamonds and other gemstones. The recent advent of the Chemical Vapour Deposition of a diamond coating on CZ or perhaps Synthetic Moissanite was mentioned to highlight the advent of recent high-tech treatment techniques and now being marketed on the internet.
After lunch the practical session began and we were allowed to handle a selection of over 200 samples of treated gemstones supplied by Çiğdem, which we viewed through a microscope. The morning theory session was put into practice and most of us found this part of the day to be the most rewarding. There were lots of ohh’s and ahh’s as we could view the treated gemstones and actually see the tell-tale signs for ourselves.
Çiğdem has amongst her collection an interesting stone nicknamed ‘The Monster’ which is a large low quality greeny/yellow cube shaped diamond and has just about all the diamond treatments possible contained all in one stone. This is a very interesting educational piece and highly entertaining to see, but not saleable enough to set and sell as a piece of jewellery, however there is a market for everything or so they say!?
A simple report like this can never do justice to such a complex subject. However, we all found this workshop session to be a revelation, valuable, enjoyable and highly appreciated. Çiğdem’s skill as a presenter inspired everyone and provided us with enthusiasm to continue with our need to keep up to date especially when looking at detecting Heat, Diffusion and Sintered cavities amongst all the other gemstone treatments.
Andrew Lamputt FIRV. May 2017.