Gem-Session 1 “True Colour”

April 22, 2011 | No Comments

Let’s kick-off this series with an interesting and buoyant theme, namely “Gems – True Colour”. As with many things , today’s world comprises modern techniques which can impact and improve the appearance of natural products, including gems. This together with the fact there are at this moment several world-wide projects aimed at improving fair-trade in the “coloured gem world” makes this not only an interesting subject but also a topical one.

If we go back in time we’ll see that beautiful natural precious gemstones were a luxurious and hence very expensive item and consequently were only readily accessible to the highest levels of society. Kings, Queens, princes and princesses and aristocracy alike were the proud owners of these elite jewels. Even then however, primitive colour improvement techniques existed which aimed to further refine the colour and clarity of gemstones. This began with the use of oils (even coloured oils) or by painting the back facets of the gem which influenced the colour when viewed from above. In short, attempts to improve the beauty of a particular gemstone aren’t just a modern day phenomenon.

To a gemmologist point of view there are two important topics now-a-days;
1. The integrity of the stones.
2. Sustainability.
By integrity of the stones we mean answers to questions like; Is the stone natural? Enhanced? If yes, enhanced up to which level? Is the colour permanent or temporary? Is the right information of treatment mentioned? Is the stone named in the right way? Hereby I would like to notice that a gemmologist will focus mainly on the stones, the jewellery-experts and jewellers will focus on all aspects combined together to protect the client and market.
By sustainability of the stones mining process & pearls culturing process we mean answers to questions like; are they mined in an efficient way with research on forehand?  With as little (permanent) on the environment as possible? Are the working conditions of the miners safe? Is the supply chain structured with an added value to be made in the country of origin?
These days there are many techniques available to create synthetic gemstones as well as those techniques that influence the appearance of gemstones. Whether it is about colour enhancements or improving the clarity of a gem. Nowadays, gemstones are frequently treated to improve their colour. One very common method used is to heat the stones. This result in stones that are inherently not very appealing becoming as beautiful as their natural high qualitycounterparts. Furthermore, these then ‘treated’ stones are cheaper to purchase purely due to their abundance.
There are however, many methods used today to improve the colour and clarity of natural gemstones, many of which are legitimate and some are dubious. A dubious example is that of the “glass-filled ruby” recently introduced in America. Originally these rubies are of the poorest opaque quality. Whilst totally impregnated with a glass-substance to become nicely looking transparent red rubies, they unfortunately cannot even endure common domestic cleaning products!  It’s clear that a client’s enjoyment of this ruby will be short-lived. If you would like to hear and see more about this subject, take a look at  this ABC Goodmorning show article.But let’s be honest, we all are of the opinion that we deserve a certain gemstone that fits to our personal budget. So the market merely responds to that fact. What we -perhaps- need to consider is.. do we really want these “improved” stones? Thankfully, natural, beautiful “True Colour” gemstones still exist, but like in the old days these stones are expensive.
With regards to the fair-trade in the gem world, there are some impressive sustainable projects running for example the “Tanzanite One” project, where in sustainable mining and education are part of the programme and the so-called Avaïki pearls. This new South Sea pearl variety is branded as a true sustainable product, therefore they will be discussed next time when “Pearls” are on the programme.

What’s so lovely about gemstones?
What fascinates me, and always did, is that nature is able to create so many divers and so many beautiful gemstones. To learn to determine gemstones (to learn to identify a gemstone with the use laboratory equipment), next to learn about their properties and why some stones belong to “the same family”, with all their specific differences still provides me joy. The site of the Museum National d’Histoire Naturelle (Paris) gives already a nice introduction. Also the American Museum of Natural History (New-York) has a beautiful permanent collection to visit, next to this they have an app for your mobile phone ; ‘Chart your own course at the AMNH Explorer’. 
Only knowing that the colour in many double refractive crystals is actually a mixture of colours which can easily been seen separately with the use of a dichroscope fascinates me. Yes, I’m talking about pleochroism (dichroism & trichroism). There are so many more optical effects which can easily be explained by a combination of their internal structure, inclusions and of course the light source you use. To give you a helping hand with regards to gem terminology you can take a look at this web-site. It’s an absolute must for everyone who would like to know more about gems to understand the associated terminology. I haven’t checked the recommended page link thoroughly but I’m certain that it provides a good start.

Cameos, intaglios and inlays

I also adore antique gem cameos and intaglios, therefore this video by the Paul Getty Museum, Los Angeles. Of course a  direct link to this museum where you can find besides their general information also their on-line collection with various beautiful cameos. You just have to add the word ‘gemstones’ and click on their search-button. The British Museum also has an impressive cameo collection, therefore also a link to their on-line collection..and add the word ‘cameo’ followed-up by a click on the search button. Also at the Museo Archeologica di Firenze, Italy, you are able enjoy a beautiful collection of impressive cammeos and intaglios…although their web-site doesn’t mention it. Another, not that often used for jewellery, typically Italian decoration technique I adore is the “Pietre Dure”, mosaics and intarsia inlays of “semi precious” gemstones, therefore the link to the museum of Semi-Precious Stone Inlays in Florence, Italy. 

For all you “starter gemmologists”  out there, I recommend  this serious compact Fun-byte; the “Gem-Kit”, a handy travel-set or for use at home! I found at the internet, but…..on a Chinese page I clearly couldn’t read! -ha,ha- So, I have no idea what the price is. Good luck! Nevertheless, if you click on the cursor while he’s on the picture then automatically the text with all the instruments of this “Gem-Kit” appears which will help you to trace it.

I’m certain that every gemmologist would agree that the most satisfying part of analyzing gems is searching for inclusions through a bi-ocular zoom microscope (which gives a stereoscopic view). The views you can obtain can be so spectacular due to the influence of different kinds of illuminations (direct light, transmitted light & dark-field illumination). The cleaner the stone is the more difficult it is to find an inclusion, the harder you have to search, the more satisfying the result will be….or an absolute disappointment. Looking in gemstones to find  inclusions (each gemstone, and even each locality, has it’s own typical specific inclusions) is unmistakably of great importance to see whether a gemstone is totally natural, enhanced, composite, synthetic …or just a piece of glass.

Besides all this I think it’s probably also interesting to tell that Gemstone certificates made by one of the known Gem laboratories world-wide is a true added value to a certain stone (piece of jewellery) or object when auctioning, assurance or estate is in focus.  For example certificates from the GIA in America,  NEL in The Netherlands and the Gem-A in The United-Kingdom.  This because it’s clear in one second for the jewellery expert where he/she is looking at plus a possible buyer can be clearly informed (even a potential oversees buyer who never has seen the stone in real life). Therefore English written certificates are preferable.

If you’re looking for education possibilities in your neighbourhood (Europe and USA), please take a look at my blog:  “Education” or “List of Gemmological Institutes & Laboratories”. There you will find direct links to all the Institutes who offer studies, courses and workshops up to the highest levels.

A little fun-byte suggestion for gemmologists both on the move and at home: GemExplorer Iphone App, by SSEF Swiss Gemmological Institute. The  App uses the Iphone’s inbuilt compass feature to show the location of gemstone mines in relation to the user’s locationwith compass arrows. The App is free and can be found via Apple’s App Store on Itunes.

My book suggestions:

To my opinion the “Photo Atlas of Inclusions in Gemstones”, by Eduard J. Gübelin & John I. Koivula, are by far the world’s most beautiful and complete books about inclusions. They are a must have for everyone who is seriously interested in gemstones. I would like to quote “..Yet the touch of genius in the photomicrography not only serves the beauty and singularity of gemstones- it also, above all, of comprehensive assistance in their evaluating identification”. For more information about this book and lectures given by J. Koivula, please take a look at  this web-site
Book details; ISBN 3-85504-095-8, Volume 3 will cost $300 (excl. tax and shipping costs). As said; the best there is! 

A book about cameos:

Because I have no ISBN-number I’ll link you trough to web-site of Herbert Wiegandt. Next to this there’s also the book “Die Griechischen Siegel der Klassischen Zeit”, an Iconographic study overview, only hard cover, partly English, ISBN 3-9806362-2-4, is available from:

I would like to thank Dr. Hanco Zwaan for his valuable input and suggestions, and for the use of microphotographs.


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Margriet Sopers

Margriet Sopers, FGA

Having a diploma in jewellery, FGA and a propaedeutic of the Academy of Art followed-up by interesting years as a jewellery expert at Sotheby's & Gemeentelijke Krediet Bank, as well as being a member for years of the Society of Jewellery Historians, I am glad to share with you today's world of jewellery.

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