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Collecting Guide: Coloured stones

By   /   July 5, 2016  /   No Comments

From rubies and emeralds to rare coloured diamonds – specialist David Warren provides an in-depth expert guide for buyers seeking a bright addition to their collection

  1. Fancy or Vivid? Get to know your terminology

A highlight in the coloured stones category — often setting world-record prices — coloured diamonds come with their own specific colour categories. A blue diamond, for example, could be classified as Faint Blue, Very Light Blue, Fancy Light Blue, Fancy Blue, Fancy Intense Blue, Fancy Dark Blue, Fancy Deep Blue or Fancy Vivid Blue. The same principle of categorisation applies to coloured diamonds of virtually all hues.

2.  Word order is important

Coloured diamonds aren’t always a single colour. You may sometimes see a diamond described as ‘Vivid Orange Yellow’ — or even ‘Vivid Yellow Orange’. But what’s the difference? The key here is to look at the last word, which will be the principal colour. A pair of Vivid Orange Yellow diamond earrings were recently sold by Christie’s in Geneva, for example, where the colour was considered marginally more towards yellow than orange.

You can also have an ‘Orangey Yellow’. Here, yellow remains the dominant colour, with just a touch of orange; it’s not as orange as an ‘Orange Yellow’.

3.  Are some colours more valuable than others?

The rarest of the rare is a red diamond — there aren’t many, and they’re generally not very big. It would be exceptionally unusual to find a red diamond above 2 carats.

4.  How are coloured diamonds graded?

Christie’s sends diamonds to the GIA laboratory (the Gemological Institute of America), which provides the world’s most trusted colour grading service. It’s often worth doing, even if you have a stone with a weak colour — particularly if the colour is faint pink, green or blue, for example, which could still be significantly valuable.

A weak yellow diamond, however, might not be, as it is not uncommon to find stones with a yellow tinge. Other colours that may still be attractive and collectable but far less expensive include brown, yellowish brown, greenish yellowish brown, brownish yellow, yellowish brownish green. There are many colour combinations — even black.

5.  Where do coloured diamonds come from?

Mining coloured diamonds is really a matter of chance. The only exception is the Argyle mine in Australia, owned by Rio Tinto, which is the only mine in the world to consistently produce pink diamonds, and is also the world’s largest supplier of natural coloured diamonds.

Diamonds in their purest form are white — as are all other gemstones, except three: opal, turquoise and peridot. What turns them a particular colour is the presence of an accidental colouring agent. A blue diamond, for example, will contain a tiny amount of boron in the composition of the stone. Green diamonds acquire their colour from radiation in the ground, while yellow diamonds are created when nitrogen enter their chemical composition. Pink diamonds result from a ‘slip’ in the stone’s lattice structure.

6.  What about other coloured stones? Is there such a thing as a perfect emerald?

When it comes to emeralds, the most coveted are a darkish green. It’s important the stone isn’t too dark, however: the highest-quality emeralds combine good colour with clarity. Imagine if you were to take an empty wine bottle made from green glass and hold it up to sunlight — that’s a good indication of the perfect shade.

The proportions of an emerald (or any gemstone) are also important. If they’re poor, light will diffract and go through the stone, rather than bouncing around within it, coming out, and hitting the eye — a phenomenon known as total internal refraction. While fissures, known as ‘inclusions’, are common, too many will affect the beauty of the stone and lower its value.

Although highly rare, it is theoretically possible to get an emerald so perfect in terms of colour, clarity and brightness that it comes close to resembling the brilliance and ‘fire’ of a diamond (I have only ever seen a handful of emeralds that fall into this rare category).

Read more at http://www.christies.com/features/Coloured-Stones-Collecting-Guide-7400-1.aspx

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