Sapphire

Sapphire is corundum, the same mineral as ruby. Red corundum is ruby; every other colour is sapphire. Blue sapphires owe their colour to traces of iron and titanium, and other elements create pinks, yellows, greens, purples and colourless white sapphires.

It is the birthstone for September. Since 1981, when a large oval Ceylon sapphire became the most famous engagement ring in the world, it has been a byword for a coloured engagement ring.

The most valued blue sapphires are a rich, velvety blue of medium to medium-dark tone, with strong saturation and little or no grey. Too light and they look washed out; too dark and they turn inky in low light.

Look for colour spread evenly across the face of the stone. Many sapphires show colour zoning, bands of lighter and darker blue, which a good cutter orients so it cannot be seen from above. Check the stone face up, and in different light.

Sri Lanka, historically Ceylon, is famous for bright cornflower blues. Kashmir’s sapphires, mined briefly from the 1880s, have a soft, velvety blue and are now among the most valuable gems on earth. Madagascar has become one of the most important modern sources, producing every shade. Myanmar, Thailand, Australia and Montana all produce fine sapphires of their own character.

Origin can affect value considerably, but it is not a measure of beauty. A fine stone is a fine stone. If origin matters to you, it should be stated on a report from a respected laboratory.

Fancy sapphires have become far more popular for engagement rings:

Teal

A blend of blue and green, often from Australia, Madagascar or Montana. Modern, individual and often good value.

Pink

From soft blush to vivid hot pink, sitting just short of ruby in saturation.

Padparadscha

A rare, delicate pink-orange, named after the lotus flower in Sinhalese. Traditionally associated with Sri Lanka, and among the most sought-after sapphires.

Yellow and green

Bright, warm yellows and soft greens, lovely in yellow gold.

White

Colourless sapphire. Durable and attractive, though without the brilliance of diamond.

Most sapphires are heated to improve colour and clarity. It is permanent and widely accepted. Unheated sapphires of fine colour are rarer and more valuable.

Some sapphires are diffusion treated, with elements such as beryllium introduced to change their colour. This is a different and less valued treatment, and it must be disclosed. A laboratory report should state whether a stone is heated, unheated or otherwise treated.

Sapphire’s hardness and toughness make it one of the best coloured stones for everyday wear. Blue sapphires look crisp in platinum and white gold, often framed by a halo of white diamonds; pinks and yellows glow in rose and yellow gold.

Clean it with warm water, a drop of neutral soap and a soft brush, then rinse and dry with a soft cloth. Never put a gemstone in an ultrasonic cleaner or a steamer.