The word Sapphire is derived from the Greek word for blue. In early history all blue gems were called sapphire, however with modern gemmological techniques, we can be more precise in categorising different gems. The blue stone we refer to as sapphire is corundum (aluminium oxide) with impurities of iron and titanium, which give the stone its colour. This varies from virtually colourless through the most desirable shades of intense cornflower blue to virtually black-navy blue. The colour in blue sapphire often occurs in bands; this is because as the crystal evolves, iron and titanium impurities are not constantly available to the crystal and hence the colour is not uniform.
Sapphire was widely credited with acknowledging the fidelity of a spouse, as it was believed to change colour if the female partner cheated! Apparently sapphires would refuse to shine for the unchaste or impure. Because of its reputation for preserving chastity, sapphire was formerly worn by priests. In the 7th Century new Cardinals of the Roman Catholic Church received from the Pope “finger rings of gold set with a sapphire to be worn on the right hand showing that the Church is now his spouse and he must never abandon her”
Corundum when pure is colourless, but different impurities give it different colours. Yellow sapphire is caused by the presence of iron. The colour in green sapphire is caused by the crystal actually consisting of very thin alternative bands of blue and yellow sapphire.
A very rare variety of sapphire is Padparadscha (named after a Lotus Blossom) which is a delicate pinkish-orange colour. It is the most rare and therefore the most expensive sapphire colour and, apart from Ruby, the only variety of sapphire to be given its own name. Padparadschas are only found in Sri Lanka and are especially popular in Japan where they fetch high prices.
Colour is the most important factor relating to the value of a sapphire. It is most unusual for stones to be sold in their natural state. Heating has been widely used to improve the colour since 2000 BC. This is still the most common of all gemstone enhancements; it is a cheap process, improving the colour and clarity of 90% of sapphires, and is permanent. Some sapphires found in Sri-Lanka are a milky white colour, called Geuda. These stones possess iron and titanium, but not in the valence states to give the stones the desirable Royal Blue colour. On heating the valence states are altered and the stones colour changes to a marketable blue.
Titanium also gives a sapphire one of its most beautiful features, that of the star-stone. When microscopic rutile (titanium oxide) needle inclusions are present and perfectly arranged at 60’ angles, they reflect light as a six-pointed star.
Sapphire is the second hardest naturally occurring substance- only diamond or another sapphire will scratch it- and as such is very useful in industry. It is used as an abrasive in emery paper, but is also used to resist abrasion-as in the bearings (or jewels) in mechanical watches. Since the beginning of the twentieth century, sapphire has been easily synthesised which results in inexpensive and uniform transparent material, which is widely used in industry. Most people come into weekly contact with a very large piece of synthetic sapphire without knowing it- the window on a supermarket checkout, which houses the bar code scanner!