A guide to buying coloured gemstone jewellery

A guide to buying coloured gemstone jewellery

It is important to always buy any gem from a trustworthy dealer. Internet recommendations and reviews can be a good starting point, as can word of mouth. Always look for members of the British Jewellers Association, the BJA, if you are in the UK. Many auction houses, such as Christie's and Bonhams, can also provide advice. Once you have found a jeweller and a stone that you like, don't be afraid to touch it and examine it closely, as many significant imperfections can be visible to the naked (even untrained) eye. This is best done in natural light, wherever possible, and it is significantly aided by the use of a loupe (a gemmologists pocket magnification glass). Comparison to other stones can also be useful and pay close attention to any treatment or enhancement the stone may have received. Most coloured gemstones have been treated in some way shape or form and this in itself isn't a problem, depending upon the type of treatment and the willingness of the vendor to disclose this to you. Common treatments include heating (mostly found with corundum stones, including rubies and sapphires) and oiling or filling to disguise surface reaching fissures (most common with emeralds). Enhancement and treatment can affect value and how you look after the stone.


(Coloured gemstone jewellery has enjoyed rising popularity in recent years)

It is always worth buying a stone that comes with a full certificate from a reputable laboratory. These include the GIA (Gemmological Institute of America), GCS lab in London, CDTEC Laboratories in Colombia, Gübelin Gem lab, Switzerland and etc. Of all the green gemstones, emerald is by far the most valuable. It has adorned the jewellery of the great and the good since the days of Cleopatra in ancient Egypt two thousand years ago and it was an important part of the treasure chests of the Mughal rulers of medieval India. The ancient associations also go far beyond the 'old world' to that of the ancient Incas of South America, who first discovered them in what is now modern day Colombia many thousands of years ago. The great natural historian Pliny the Elder observed in the first century AD that "no stone has a colour that is more delightful to the eye, there being no green in existence more intense." With emeralds it is the depth of colour that is crucial. Too light or too dark and the stone's value begins to drop. Vivid green is the ideal colour, best described as resembling a green wine bottle when held up to the sun.

Emerald Stone

(Emeralds are the most valuable coloured gemstone)

Emeralds from different origins tend to have subtly different characteristics and the most highly regarded Colombian stones often contain a hint of blue or yellow. In terms of clarity, most coloured gemstones are not as 'clear' as diamonds. The fewer and the smaller the number of inclusions within a stone, the greater its value. Emerald inclusions are often described as looking mossy or garden-like"jardin". The position of the inclusions within the stone can also have an effect on the types of setting that can be employed and also how visible they will be once the stone is mounted. Rubies have enjoyed a good deal of interest throughout the centuries and much has been made of the blood red appearance in much ancient philosophy and mythology. They also earned a religious significance and the Hindus for example referred to the stone as the "king of the gemstones" and the "sun new risen" that "paints the whole house with crimson." The famous 'pigeon blood' rubies of Burma command the highest prices but they are also produced in many other parts of South East Asia and East Africa.


(Rubies and diamonds set into a colourful necklace)

Rubies actually vary quite significantly in terms of their colour, from brownish-red to oragey-red to purplish / pickish-red. Rubies are from the corundum family and are identical to sapphires in every way except colour (rubies are in essence 'red' sapphires). As with emeralds, the best colour is one that is not too dark or too light and evenly distributed throughout the gemstone. The most sought after are vivid crimson in appearance with a hint of blue. Rubies from difference origins have unique colours, the Mozambique ruby for example is usually pinkish-red. With coloured gemstones transparency is more relevant than clarity, as almost all coloured gems contain some form of inclusion it is the position and appearance of these inclusions that determine their effect on value rather than their mere presence. If a coloured gem is faceted inclusions are more easily 'hidden' in the cut than they are with cabochon stones. As discussed in earlier articles, some corundum can contain a rare inclusion known as an asterism (derived from the Latin for star) which is formed from the mineral rutile present only in cabochon cut stones.


(Sapphire jewellery is highly in demand)

Rubies and sapphires a 9 on the Mohs scale of hardness of 1 to 10, only diamond is harder with a score of 10. This gives the cutter plenty of options to work with but cushion, oval and round tend to be the most popular cuts because they optimise the light reflecting characteristics to greatest effect, minimising 'extinctions' or dark patches within the stone. In fact, to the trained eye, the quality of the cut is an indicator as to quality of the stone, as sellers tend to put more effort into cutting the finer stones they know will fetch a higher premium. Good proportions and symmetry are important and it should not have any hard edges. A well cut stone will possess a desirable lustre, which in rubies is known as "bright vitreous." Treatments and enhancements are common practice with coloured gems so it is important to buy a certified stone. The vast majority have received some form of treatment, mainly heat treatment in the case of rubies and sapphires and oiling or filling with emeralds but they can also include dyeing, irradiation and diffusion. Lattice diffused sapphires can be any colour and not always detectable, sometimes can be detected by immersing the stone in water and observe it under microscope. In some cases the colour penetration is shallow and it is likely to see colour concentrate along the facet junctions and girdle edges. Or in others, it goes all the way into the stone. The presence of joining lines in a ruby could also indicate a 'composite' stone, whereby a natural ruby has been combined with synthetic material to increase its size and colour. Whilst it is possible to detect most treatments and enhancements it is recommended that buyers seek the advice of professionals when purchasing coloured gemstones.
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