Discover the science of gems with Tanja Sadow (Part II)

Dominic Fondé is a freelance artist living and working in Singapore. He specialises in glass engraving, creating artworks for private clients and gallery sale. He also teaches regular classes in glass art. To find out more about Domonic and his artwork, please email him at

As promised, here’s part II of ‘Discover the science of gems with Tanja Sadow‘. It is the evening of 14 December and Tanja Sadow, Dean of Jewellery Design and Management International School, is giving a talk as part of the Science in the Café series. Starting with the difference between a mineral and gem, Tanja highlights the complexity of the gem world.

There are new minerals discovered every year, and as a result the number of known minerals is now over 4,000. Very few of these would be classed as gems. Chemical composition, crystalline form, durability and rarity are all factors in defining a gem. Beauty is obviously a factor too, but it is rarity that causes the first surprise of the evening. In our first meeting, Tanja had teased the audience with the question: “What is the most expensive gem on the market?”

Like most others in the audience, I immediately thought of the diamond, but this was incorrect. The most expensive gem turns out to be the emerald! The factors that define the value of a gem are tone, hue, saturation, clarity and cut as well as overall weight. Clarity, tone and hue are among the most important characteristics of this gem, but due to its rarity, it can often command a higher price than diamond.

The grading and valuing of gems follows rigorous lines with ‘cut’ having significance both on the aesthetic and monetary value. Tanja discusses the colour grading system of diamonds. At the top of the scale, the differences are so minute that only the most highly trained individual can distinguish between them.

Diamonds, Source: Mario Sarto

Tanja makes it very clear that one of the most important aspects of choosing a gem or a piece of jewellery is to ask yourself, “Do you like it?” The angles of the facets of a brilliant cut diamond have been mathematically calculated to reflect the maximum amount of light back to the eye of the viewer.

These calculations were done way back in 1919 by Marcel Tolkowski (also recorded as ‘Marcel Tolkowsky’ in some sources), but just because we know the exact angle, it does not mean that every diamond is cut to the exact same shape. The skill of the diamond cutter is a big factor. If he is even slightly inaccurate with his cut, the gem may appear dull, significantly affecting its beauty and value.

Next she talks about pearls. Pearls are layer upon layer of secreted material formed inside a mollusc when an irritant such as a grain of sand lodges itself inside the flesh of the creature. The chances of finding one can be rare, yet there are thousands of them for sale all around the world.

Pearls, Source: Abhinaba Basu

Tanja explains that that these are not natural pearls but farmed or cultured pearls. A cultured pearl is created when a specially produced nucleus is deliberately placed inside a pearl. The pearls are then allowed 1-3 years to secrete nacre over the surface of this nucleus to produce pearls, in a fraction of the time compared to the natural process which takes longer with grains of sand or other stimuli introduced by natural causes. Man can come up with some fairly convincing imitations of most natural wonders.

“True or false?” Tanja asks. “Can you tell a cultured pearl from an imitation if you rub the pearl against your tooth?”

This may sound like a joke, but believe it or not, the answer is ‘true!’ A cultured pearl will have a rougher surface compared to a man-made imitation, and the nerves in your teeth are so sensitive, that they arean ideal tool for realising this distinction.

“What about fake gem stones?” someone asks? Well what exactly do we mean by fake? Tanja passes around a small but gorgeous purple stone which we all admire and many assert that it is amethyst. She drops it into a small pot of a mysterious chemical. The refractive qualities of this liquid bend the light and reveal that this purple stone is in fact a triplet: a layer of coloured cement sandwiched between two layers of quartz!

Cut Amethyst

With gem simulants (materials that look like more valuable gems), it is sometimes possible to perform some quick tests to ascertain their nature. Much harder to spot though are laboratory-made synthetic gemstones. While some of these are used for jewellery, the majority of these stones are created for use in the industry, having applications in everything, from coating saws and drills to enhancing the power of lasers.

By now it is getting late and the session comes to a close. We all head home, heads buzzing from all the new things we have learnt and with eyes like saucers from viewing the amazing gems that Tanja brought with her. It is no wonder that she talks about them so enthusiastically. They really are as fascinating as they are beautiful.

You too can learn more about the fascinating world of gems and jewellery design. Just give the Jewellery Design and Management International School a call to find out about their classes and schedules. You will find their contact details at

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