Buying coloured gems - 12 things to think about

Buying coloured gems - 12 things to think about

Whether you are interested in rubies, sapphires, coloured diamonds or emeralds, consider the 12 points below to ensure you enter the market place fully equipped:

  1. Terminology and jargon

A liberally shared commodity between gemstone and fine jewellery experts. When it comes to describing the intensity of colour within a stone, there are some standard descriptor words to look out for with diamonds: 'Faint; Very Light; Light; Fancy light; Fancy; Fancy Intense; Fancy Dark; Fancy Deep; Fancy Vivid.' These are prefixes to the colour, so for example you may be presented with a stone that is described as a 'Fancy Vivid' pink, which would fetch a price many orders of magnitude higher than a 'Faint' pink. This applies to diamonds of all colours.


(Intensity of colour is one of the most important factors to consider when buying coloured stones)

  1. Many diamonds are multi-coloured

When presented with a diamond described by more than one colour, it is the last word that indicates the dominant colour. This can have a profound effect on the value of a stone, as for example a 'brown-pink' will be worth significantly more than a 'pink-brown,' due to the levels of demand for the dominant colour in each. You can also find suffixes containing 'ish' and 'ey,' such as 'brownish-pink' or 'orangey-pink,' whereby the last colour is still the principal one but there is a small hint of the first colour, just to a lesser degree than one would find with straight 'brown-pink' or 'orange-pink.' 'Ish' and 'ey' are actually more commonly found than straight colour combinations.

  1. The hierarchy of colours

 With all precious coloured gems, some colours are significantly more valuable than others. Red diamonds are by far the rarest, and most valuable, closely followed by pinks and blues (there is some disagreement within the industry as to whether it is the blue or pink diamond that truly sits in second place). Diamonds also come in yellow, green, orange, brown (sometimes marketed as 'Champagne' or 'Cognac') and even black. Of course any combination of the above is also possible. With other coloured gemstones, it is also the depth of colour that has a significant effect on the value. Emeralds come in green, bluish green and yellowish green and the Colombian varieties fetch the highest prices. Rubies are always red but their sister corundum stone, the sapphire, is primarily found in yellow, blue and pink (although there are some to be found in almost every colour of the spectrum).


(You can find gems in almost any colour of the spectrum)

  1. Coloured gem Certification

 There are hundreds of certification labs dotted across the globe, although most are centred in hubs of the gemstone trade, including London, Antwerp, Ramat Gan (Tel Aviv), New York, Colombo and Jaipur. The GIA (Gemmological Institute of America) are by far the most well known diamond certification lab (although they do also certify other stones). Probably the most renowned non diamond coloured gem certifier are Gübelin, based in Lucerne, Switzerland. However, many smaller labs, such as WGI and GCS in London, have developed a reputation as a more cost effective alternative for less high value stones. CDTEC are the Colombian government recognised laboratory for emerald certification in the country's Boyacá Department (the principle emerald producing region of South America).

(See the earlier article: 'Certification: the art of the 5th 'C')


(GIA & Gübelin have established themselves as lead gem lab for diamonds & emeralds respectively)

  1. Origins of coloured gemstones

Diamonds in their purest form are white, as are all other gems except opal, turquise and peridot. The colour that appears in the 'white' gemstones comes from the accidental input of a colouring agent. For example, pink diamonds are caused by a movement in the stone's internal lattice structure, blue diamonds by the inclusion of trace elements of boron, green from radiation and yellow from the presence of nitrogen. Emeralds and rubies are coloured green and red respectively due to the presence of tiny amounts of chromium or varadium and sapphires are coloured by small quantities of  irontitaniumchromiumcopper, or magnesium in their crystalline structure.

  1. The quality of emeralds

With emeralds, the value comes from a combination of the clarity of the stone and the right depth of colour as well as the amount of oiling the stone has received. The highest value emeralds are not too light or too dark, the closest analogy would be a green wine bottle held up to bright sunlight. With emeralds the proportions of the stone are very important, as the internal refraction of light within the stone cause it to literally radiate light. Where fissures or inclusions reach the surface, light cedar oiling can fill these and improve the appearance of the stone. However resins and heavy oils can decrease the value of an emerald whilst improving its initial appearance so you have to be careful!

  1. Rubies and sapphires

Rubies and sapphires have grown in prominence in recent years and many of the principles that apply to emeralds are also relevant when buying these stones. A tiny percentage of the highest quality rubies have a dark red depth of colour that is referred to as 'pigeon's blood,' which can be likened to a warm burgundy, and these fetch the highest prices.


(Rubies, sapphires and emeralds currently make up 10% of the precious stone market and rising)

  1. The importance of origin

 The origin of a coloured gemstone cannot be underestimated when determining its value. The finest emeralds hail from Colombia, the best rubies from Myanmar (Burma) and the most desirable sapphires come from Kashmir. That's not to say you can't find high quality examples of each from elsewhere in the world.


(The finest, and most valuable, emeralds originate in Colombia's world famous Boyacá Department)

  1. Does size truly matter?

Buyers of fine stones often get caught up in the perceived importance of carat size. When considering a purchase, always take the '4 C's' into account (colour, clarity, carat and cut). Only through consideration of all 4 can the true value of a stone be accurately assessed.

  1. Buying treated coloured stones

There are a lot of misconceptions on this topic. People have been treating stones for millennia and it does not always compromise a gem's value, in fact it can enhance it, depending upon how it is done and type of treatment that is carried out. Emeralds are usually graded from 'No Oil,' through 'Minor' or 'Insignificant' oiling, 'Moderate' oil to 'Significant' or 'Heavy.' No oil stones attract a premium that can be as much as 40% above a minor oil emerald. Heavy oiling and treatment with resins should be avoided. When it comes to rubies and sapphires, over 90% have experienced some form of heat treatment so it is very uncommon to come across a totally untreated stone.

  1. Treated or 'enhanced' coloured diamonds

When buying coloured diamonds check the certificate careful and only buy 'natural' stones. One thing to look out for with green diamonds is that they are sometimes 'radiated' in a laboratory rather than in the ground, substantially weakening their value. Various heat treatments and radiation techniques can be used on diamonds, both to enhance their colour and to remove inclusions under the surface.


(90% of rubies are heat treated in some way, often this is done by centuries old tradition methods) 

  1. Looking after coloured stones 

When it comes to caring for diamonds most people are blissfully unaware that they can actually break, chip and sustain lasting damage. The 'hardness' of a stone is measured by way of the Mohs scale and it is important not to allow diamonds to scratch one another if they are stored or transported together. The same is true of sapphires and other gemstones. It is also worth considering the fact that emeralds can be very brittle and should be treated with care to avoid chips and scratches that can ruin the appearance of the stone and result in it needing to be re-cut and polished, diminishing its overall carat weight.
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