The sapphires belong the corundum group (which includes rubies) and which is characterised by their excellent hardness, whilst the high refractive index of 1.76 guarantees spectacular fire in well-cut, high quality examples. Mined for the past 3,500 years in Myanmar they have a long history, rising to prominence during the Roman Empire.
The gemstones in the corundum group consist of pure aluminium oxide that crystallized into gemstones as a result of pressure and heat at great depth. The presence of small amounts of other elements, especially iron and chrome, are responsible for the colouring, turning a crystal that was basically white into a blue, red, yellow, pink or greenish sapphire.
Most blue sapphires show inclusions or uneven colour distribution. Like rubies, high quality sapphires show fine, hair-like inclusions of rutile, called silk, that do not interfere with the transparency of faceted gems. The finest sapphires, though not as valuable as comparable rubies, are still extremely valuable in sizes of over 10 carats. Of all the colours, the top-grade blue sapphires are the most valuable, followed closely by the orange-pink padparadscha. Connoisseurs regard the Kashmir colour with its velvety shine as the most beautiful, and most valuable, blue. Due to traces of iron and titanium this is typically a pure, intense blue with a very subtle violet undertone, intensified with a fine, silky shine. Prices for Kashmir blues, in sizes over 20 carats, have exceeded USD130,000 per carat.
However, the Burmese colour is also regarded as particularly valuable. It ranges from a rich, full royal blue to a deep cornflower blue. The oldest sapphire finds are in Sri Lanka and it remains an important source of supply, together with Cambodia, Madagascar, Tajikistan and Thailand.
Cutting sapphires is especially challenging. Not only is the stone extremely hard but, depending on the viewing angle, they also have different colour and intensities. The cutting process has to orientate the raw crystals in such a way that the colour is brought out to its best advantage. The bright light of day makes most sapphires shine more vividly than the more subdued artificial light of evening. So in fact it is not, as is often claimed, the darkest tone that is the most coveted colour of the blue sapphire, but an intense, rich, full blue that still looks blue in a poor artificial light.
Heat treatment of blue sapphires is now a widespread practice that renders untreated sapphires all the more valuable. The blue colour can be enhanced with properly applied heat that rearranges the atoms of the gemstones. Very dark blue colour can be lightened at 1,200 degrees C for a few minutes whilst more opaque or unevenly coloured sapphire can also be improved.
The star sapphires are another rarity, half-dome-cut sapphires with a star-like light effect that seems to glide across the surface of the stone when it is moved. Star rubies and sapphires show a bright six-legged star in the dome of their cabochon. The stars, like the eye of cat’s-eye, are formed by light reflecting off tiny inclusions in the stone.
According to market research, blue is the favorite colour of some fifty per cent of both men and women. No doubt this underpins both the demand for high quality sapphires and the prices that are now being reached for fine, untreated examples. At Damian By Mischelle we confess to having a particular weakness for this stunning stone, both in our private collection as well as in the pieces on offer to our clients. We have a number of rings and necklaces set with 10 carat to 30 carat blue sapphires. Our supply network also brings us some particularly fine examples that include white, green, yellow and occasionally pink.