Eric C. Emms, FGA DGA Ltd  

ericemms@aol.com

07973 725 266

34 Ely Place, Suite H 4th Floor, London EC1N 6TD, UK

Eric writes non-technical gem-related articles for gem industry publications. See the menu on the left for a list of a few published in the past. The following are two recent examples:

Diamond, Simulants and Synthetics  

A simulant of diamond is a stone that looks like diamond but has different chemical properties (unlike diamond not made up of carbon atoms), physical properties (dissimilar values for hardness, density and thermal conductivity to diamond) and optical characteristics (e.g. lustre, refraction and dispersion). 

Common simulants are synthetic cubic zirconia, usually referred to as CZ or sometimes as “cubics”, a very cheap but effective imitation composed of zirconium dioxide; and synthetic moissanite, an increasingly popular manufactured stone. Other less common simulants may be encountered, such as colourless synthetic spinel, YAG and GGG (good simulants sold in the 1970s prior to the mass marketing of CZ) and glass, found in most costume jewellery, sometimes called paste.  

So what to look for with a jeweller’s lens? Examine both the surface and the interior of the gem. Diamond is the hardest known material so when cut and polished takes an extremely flat surface. Where two facets meet (say a star and a kite facet) the edge will be extremely sharp. Facets seen on simulants have more rounded edges. Keep a CZ and a moissanite sample and regularly compare each with a diamond. It may take a while to practice this identification technique and once mastered is extremely beneficial. 

Take note that diamonds exposed to a great amount of wear over the years may show abrasions on their sharp facet edges. Such abrasions are seen commonly on old cut gems (old English and old mine brilliants) and should not be taken as evidence of the gem not being a diamond. Moissanite is a pretty hard simulant so the rounded facet edges are harder to discern although I find moissanite is easier to spot than CZ. Moissanite, unlike the other simulants mentioned above, exhibits double refraction. Just look for a doubling of images (say the pavilion facets meeting at the culet) when examining moissanite through a kite facet. To my eyes moissanite of appreciable sizes (say over half carat) show a tell-tale yellowish green colour. Most simulants tend to being ‘loupe-clean’: no inclusions are noticeable using a lens whereas most diamonds contain crystals, feathers, and clouds etc, inclusions an experienced eye readily identifies.  

You should be aware of gem quality synthetic diamonds being sold in the UK market. A synthetic diamond is a diamond grown artificially in a factory. Synthetic diamonds have been called man-made diamonds, cultured diamonds, laboratory-created diamonds and laboratory-grown diamonds. Most examples seen are yellow to yellowish brown and may be mistaken for natural fancy coloured diamonds. Synthetic gem diamonds have the same chemical properties (pure carbon with nitrogen as an impurity) and physical properties (refractive index, hardness and density) as natural diamonds, so a pawnbroker, jeweller or dealer will not be able to identify them using standard gemmological equipment. However gem quality synthetic diamonds do exhibit sufficient differences to natural diamonds for a gemmologist to identify them. Briefly these differences are a characteristic yellow-brown colour (although colourless and blue synthetic diamonds have been grown but are rarely encountered), angular colour zoning and metallic inclusions unique to synthetic diamonds and a characteristic response to short-wave ultra-violet light. 

You should be aware that synthetic diamonds exist, know how they can be identified and how to describe them to a consumer. Please contact us for information of diamond courses we run.

The New Gemmology  

Whenever I present a coloured stone seminar or a short practical diamond grading course there is normally at least one participant who has never held a loose precious stone in their hand. Following their initial excitement in handling the gem, usually in the form of gasps of approval and much moving of the gem to catch the light and admire the full beauty, one of two questions (or both) normally is asked of me: “Is it real?” and “How much is it worth?” These two primary questions reveal the most emotive elements the consumer instinctively feels about gems.  

Let’s develop these themes. By asking the first question the consumer, when considering a gem or gem-set jewellery purchase, wishes to be reassured of the authenticity of the gem: “Is it real or is it a fake?” the prospective buyer of a ruby ring may ask. Without wishing to re-ignite continuing debates within our industry on the precise definitions and negative consumer perceptions of the words ‘simulant’ and ‘synthetic’, it is clear to me that all of us in the gem and jewellery industry must be able to answer fully this fundamental first question posed by the consumer.  

An obvious supportive reply to the question may be “Yes, the ruby is natural. Not a man-made ruby or something that looks like ruby” Our response immediately raises the gemmological subjects of accurate gem identification and unambiguous description. We must be in no doubt the ruby is not man-made by testing the gem ourselves, using our gemmological expertise to confirm genuineness and/or asking a competent gemmological laboratory for a report attesting to its authenticity.  

So now the would-be ruby consumer is confident the gem of interest to him or her is a genuine ruby. (As an aside, coloured stone jewellery pieces displayed in the windows of a retail store close to where I live in central London are labeled as “real stones”: an interesting adjective, note not “genuine” or “natural”, words we in our industry employ, but “real”, a word a consumer draws on as in the first question posed). If a consumer is confident in genuineness, how should the ruby be described if it has undergone some form of treatment?  

Perhaps the ruby has been heated, or its surface reaching fissures healed by “flux”, or any surface cavities filled with “glass” or fissures have been filled with “glass” or the ruby may have been stained with dye or coloured oil? Is a ruby treated by any one of these modifications still to be described as a “ruby” to a buyer? As an example, consider a ruby heated and its fissures filled with glass to improve its appearance: is this modified gem still to be thought of by seller and buyer as “natural”?  

Of course, we can refer to published recommendations issued by the World Jewellery Organisation (CIBJO), the American Gen Trade Association (AGTA), the Laboratory Harmonisation Manual Committee (LHMC) and other authorities on what may be called a “ruby”, a “natural ruby”, what enhancements need to be “disclosed” and how gem laboratories may describe such treatments on their reports. But within our industry I do not see absolute agreement on these definitions. I am, at present, not certain what a “natural ruby” is anymore: pity the poor consumer!  

When we address our consumer’s second question “How much is it worth?” we consider the gem’s price - so many US dollars for the stone. Yet price follows from value, and establishing value only comes from ascertaining quality. It follows when answering the second question we must be able to communicate effectively the quality of a gem to the consumer.  

With colourless diamonds a useful pointer to quality is the so-called 4Cs. However carat weight, colour, clarity and cut does not convey fully the beauty of a diamond. The brightness, dispersion and scintillation of any polished diamond cannot be expressed in terms of the 4CS or of a “cut grade” or indeed by all the information listed on a diamond grading report. On a personal level, I find antique diamonds fashioned in the old mine brilliant style most aesthetically pleasing, yet such diamonds may score poorly if judged by modern ideas of quality.  

With coloured stones quality generally can be defined best by reference to colour and rarity. Each of us, whether we be a miner, gem dealer, gemmologist, gem valuer or retailer, must be prepared to contribute in explaining these factors to the would-be consumer. We need to demonstrate the wide range and depths of colour seen in rubies and we should show the relative rarities of an untreated ruby and the various treated rubies considered above. How best to express these factors to the consumer?  

Increasingly we must be prepared also to discuss the third likely consumer question: “Where do you source your gems?”

Gemmological education arms us with facts so we can understand and identify the plethora of diamonds, coloured stones, pearls and cultured pearls. The new gemmology, as I phrase it, must go further. Gem facts and figures and correct methods of identification are crucial for a successful basis in classical gemmology but today we must also learn to communicate. The new gemmology will require us all in answering actively consumer questions on gems and demonstrating authenticity and quality of coloured stones to the prospective purchaser in an engaging and enthusiastic manner. Do all of us have the understanding, inclination and fervour for this important undertaking?