Traditionally we associate sapphires with the colour blue, however there is a whole other world of naturally occurring fancy coloured sapphires that many people aren’t aware of, a rainbow of which can be found in our evolving collection of antique and vintage engagement rings.
Sapphires are the second hardest gemstone to diamond and have been used in jewellery for centuries. They are part of the corundum species of gemstones comprised of aluminium oxide, shared only by ruby. In its pure form corundum is colourless, and when certain impurities are present, colour is created.
The small amounts of metal oxide impurities in the chemical makeup of corundum are called the colouring, or trace, elements. Their presence is one of the main reasons we see colour in gemstones. When chromium is present, red is produced to form rubies, and blue in sapphires is due to the presence of iron and titanium - differing degrees of these produce a variation of blues. The fantastic fancy colours are caused by a mix of other elements, namely chromium, iron and titanium for purple or violet hues; iron for yellow sapphires; iron and chromium for orange; low chromium traces for pink; and a mixture of other elements for green, brown and black.
Most fancy colours and pastel shades of sapphires are from Sri Lanka, but they are also found in Burma, Madagascar and Tanzania. The most prized of the fancy colours are Padparadschas. Padparadscha sapphires are a subtle mixture of pinkish orange to orangey pink, some describe as almost a salmon colour, due to chromium, iron, and titanium. They are very rare and are the only variety of corundum other than ruby to have their own name. Their name is derived from the Singhalese word for lotus flower, and these are highly desirable.
Star sapphires are also seen in more fancy coloured stones, for example opaque pale blues and darker purple or mauves. This optical phenomenon showcases a shimmering star effect on the top of the stone when in the right light, which is quite spectacular and rare. This shimmering effect is called asterism and is due to the orientation of inclusions within the stone.
Today colour intensity, optical phenomenon and even the actual colour hue can be altered and created by various treatments. To see a naturally occurring and unenhanced sapphire is becoming increasingly hard to find. The unique quality of fancy coloured sapphires is what can make a piece of antique jewellery even more special, their true value lies in that they are how nature intended – colourful!