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Gem Stones


This page gives you general information which I hope will be useful in helping you to know what you are buying when you look at coloured gem stones.

I’m also adding a page about each specific gem stone that I set in my jewellery and you can jump straight to these pages from the list below. There are only a few at the moment but the list will grow as I find time to add new pages.

Generally …

Coloured gem stones fall into two categories: Precious and Semi-precious. The distinction rests primarily on rarity but there is also a traditional aspect. Precious stones are generally held to be Diamond, Ruby, Sapphire and Emerald although other stones have been included in this category at other times in history. You can see that this is, in some ways, an arbitrary classification when you consider that Emerald is a green colour of the mineral Beryl and is considered to be precious whereas all the other colours of beryl, blue, (aquamarine) red (bixbite), yellow (heliodor) and pink (morganite) are all considered semi-precious. The list of semi precious stones is huge. It’s basically anything that’s pretty but not on the precious list.

As with diamonds, coloured gemstones are graded by various different qualities:

Cuts


Traditionally it was the clarity of a stone that determined how it was cut with clear stones being facetted and opaque stone cut ‘en cabochon’. Another factor, however, is hardness, as facets cut into soft stones will tend to wear away over time and the surface will become scratched and dull. Despite this, clear stones are also cut en cabochon, especially where the design of the piece demands smooth regular lines. Cutting a clear stone like this will emphasize the richness of its colour whereas faceting the stone will emphasis it’s clarity by causing it to sparkle.

Hardness

The hardness of a stone is measured on a scale of 1 to 10. This scale is known as the Mhos scale and was developed by the famous bar man featured in the television series, ‘The Simpsons’. (maybe) Each place on the scale is represented by a mineral of that hardness with Talc at number one (Please note, blokes, it’s not ‘hard’ to use talc) and diamond at ten. As a rule stones with a hardness less than 7 would be more suitable for cutting ‘en cabochon’.

It’s worth mentioning that Mohs developed his hardness scale in 1812 and it’s a relative scale rather than an absolute one. It’s based on which minerals will scratch other minerals rather than anything more fundamental. For instance, corundum is twice as hard as topaz, but diamond is almost four times as hard as corundum yet there is only one step between each of these three minerals. The table on the right shows both Moh’s scale and actual hardness

For practical purposes, you want to choose stones that will withstand the rigors of everyday wear. Facetted emeralds are a popular choice for rings but, at hardness 7.5 you’re going to find that the facets wear off much faster than either a sapphire or ruby both of which are hardness 9. For earrings and pendants, of course, this is not such an issue seeing as these pieces come in for much less wear.

Colour

The colour in a stone is often due not to the properties of the base mineral itself but to the impurities within in. As I said above, Beryl comes in various shades with, for instance, the green colour in emerald coming from traces of of chromium and sometimes vanadium within the stone. Likewise, amethyst is a quartz but iron and aluminium impurities combine within the stone to produce a graduated purple colour. If you find amethyst ‘in the wild’ as it were, you’you’ll see that the crystals have the characteristic hexagonal quartz shape. In some cases they are clear at the base and slowly graduate to a purple colour that intensifies near the top of the crystal or else they are clear on the inside and the colour deepens towards the outer edge. This shows that the impurities came into play late in the crystal’s formation and only contributed to the colour as the mineral cooled. (the base of the crystal forms first and the crystal ‘grows’, narrowing to a point as the material building the crystal is depleted).

The fact that the colour is due to impurities and is affected by the cycle of cooling means that a consistent deep colour is rare and prized within gem stones. As the colour is often graduated, finding a large volume with a consistently rich hue tends to be very rare. This is why the price of coloured stones rises exponentially with size and why the richest colours command the highest prices. Ruby, for instance comes in all shades of red from almost black to a washy pink colour. The premium colour for a ruby, however, is known as ‘pigeon-blood red’ and, as its name implies, it’s a deep rich red colour that retains the clarity and lustre of a liquid.

Clarity

Naturally formed stones often have inclusions or flaws. These are either small pockets of other minerals that get caught in the crystal as it cools, or else cracks and fissures in the material. Some stones are much more prone to inclusions than others and emeralds in particular suffer from these impurities which are sometimes called ‘jardin’ from the French for garden. (Why? I don’t know). These flaws are generally accepted in emeralds, and stones with high clarity are very rare and can cost more than a diamond of equivalent size.

You may well find inclusions in other stones and, if you do so you have to take a view on whether it mars the appearance sufficiently to reject the stone in favour of another one. The thing to watch out for is a stone that should be clear but appears dull or hazed, indicating that the material is of generally poor quality. A small black spec at the margin of a deep blue sapphire, on the other hand, isn’t going to materially effect the performance of the stone.

One other thing to be aware of is that stones are often ‘oiled’ in the lapidary trade. This involves applying an oil of similar refractive index to that of the stone, which is drawn into the fissures in order to fill and hide them. It’s common practice and, so long as the oils used are not coloured, it is accepted within the trade but you might want to ask whether the stone you are buying has been oiled, especially if it is an emerald as, if you were to have a jeweller work with the stone, he or she would need to know about it.

So, this is all very interesting but how does it relate to jewellery?

If you are planning on using coloured stones in your jewellery then you consider the following:

Hardness:

If it’s a ring, a bangle or a bracelet then you might want to steer clear of the softer stones as all these pieces tend to take a bit of a battering from the environment. Opals are lovely but they are also soft and friable and, whereas they will often survive on a ring where the claws can offer some protection, you wouldn’t’t want them in a bangle which is going to clatter around on the desk every time you put the phone down.

Cut:

These days the cut of a stone is more a matter of style and preference. Whereas there would be little point in faceting an opaque stone, clear stones are often cut cabochon in order to fit in with the style of the piece. If you like clean line then a cabochon set in a rub-over setting is probably going to please you more than a claw-set facetted stone. (click here for more on settings)

Colour:

As discussed above, each stone has a premium colour which will command a higher price than other shades. However, once again it’s a matter of preference as to which shade you choose. In the Victorian era there seems to have been a penchant for sapphires the colour of coal. Nice. Then in the 1980’s when I was cutting my teeth in the jewellery trade, the pale ‘Ceylon’ sapphires were all the rage. Currently these tend to be seen as a little too watery and there is a move back to the deep velvety royal blues that, unfortunately, cost rather more. Choose your colours according to what you think works well for the piece and what will work with the clothes and accessories that you tend to wear and try not to be led by fashion as you know that it will all change again in five years time anyway.

Clarity

If you are using a clear stone then make sure that it appears lustrous and vibrant. If it’s a cabochon then it should look like a drop of liquid; if it’s a facetted stone then the light should dance within the stone giving a definite sparkle.

Once long ago most jewellery was built around the precious stones. Stones were often a form or currency and a compact way of carrying your wealth around and so the settings were minimal and were largely there to display the stones. These days, when wealth is spread a little more thinly and people wear jewellery for the joy of the design and not just as an ostentatious display, stones tend to be smaller and are used more to enhance the design than to be its centre piece. None the less, if you have the chance to choose your stones then careful selection can make a huge difference to the overall impact of your jewellery.

18ct gold diamond and rubelite bangle

In my own jewellery I tend to use diamonds in my gold and platinum work and a small range of semi-precious stones in the silver and gold work.

I like strong vibrant colours and this dictates my choice of stone more than anything else. For most of my pieces you can choose alternatives so if there is something that you particularly like then please ask.

If you’re commissioning a piece then you may have stones of your own that you would like me to use. I’m always happy to do so but I would want to examine the stones carefully in order to verify that I’m happy to work with them. The last thing that I want to do is crack the priceless sapphire that’s been handed down in your family for hundreds of years!

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