Sapphires are one of the hardest minerals on earth after diamonds, and they come in a gorgeous rainbow of colours. They are hardwearing and make excellent stones to set into jewellery, and sapphire rings and sapphire pendants are perennially popular.
What are Sapphires?
Sapphires are members of the corundum family, and come in every colour except true red - red corundums are known as rubies. They are very hard - coming in at a 9.0 on the Mohs hardness scale - which makes them an excellent choice for jewellery.
History and Lore of Sapphires
Sapphires have been known to history for millennia, although it is thought that the stones referred to in the Bible and by Greek and Roman writers may have been lapis lazuli. By medieval times, stonecutters were referring to blue corundums by the term ‘sapphire’, derived from the Latin sapphirus meaning ‘blue’.
In Greek and Roman times, sapphires were thought to protect the wearer from envy and harm. Later, with the ascendancy of the Roman Catholic Church, sapphires were seen as stones of heavenly blessing and bishops of the church wore rings of gold and unengraved blue sapphire.
In modern times, sapphires are most associated with wisdom and insight. Blue sapphires are associated with royalty, especially since Lady Diana Spencer’s famous blue sapphire engagement ring, which has now been passed down to her daughter-in-law, Catherine, Duchess of Cambridge.
Sapphires are the birthstone of September babies, and of the star sign Virgo. They are also the stone of the 45th wedding anniversary.
Types of Sapphire
In addition to the most commonly identified blue colour, sapphires come in many other colours, including a few very special types. They can be violet, green, yellow, orange, pink, black, or purple, and these colours aren’t uncommon, although some are hard to come by in pieces larger than one carat. Colourless sapphires are quite rare. They are the most pure form of corundum, and have been used as diamond substitutes in jewellery.
The padparadscha sapphire is a rare pinky-orange variety named for the Sinhalese word for lotus flower. It was originally found in Sri Lanka, although there are also small deposits in Vietnam and East Africa. Natural padparadscha sapphires are the most expensive of the fancy sapphire colours.
Star sapphires are an interesting stone - the stones display asterism, a phenomenon in which small thread-like inclusions in the stone form a six-pointed star. These stones are cut into cabochons to show off the star, and can be very beautiful.
Particoloured sapphires are sapphires that have more than one body colour, and are fairly rare.
Colour-change sapphires are very rare, and show one colour under natural light and another under incandescent lights. They are usually blue in natural light and purple under incandescent lights, or gray-green in natural light and pink to reddish-violet in incandescent light.
Common Sapphire Treatments
It is very common to heat-treat blue sapphires to enhance their colour and reduce ‘silk’ inclusions, to the point where it is usually assumed that sapphires sold in stores have been heat treated unless they are certified as having no evidence of heat treatment. Depending on the heating and cooling method, heat treatment can also make silk inclusions stronger, giving more prominent asterism to star sapphires.
Some sapphires are fracture-filled, meaning that surface-reaching cracks or cavities are filled with a substance, usually glass or resin, to improve clarity and stability.
Lattice diffusion is also sometimes applied to sapphires, to give them a more vibrant colour. Lattice diffusion is where a natural stone is heated in the presence of another mineral, in this case usually beryllium, to push the mineral atoms into the natural stone and change its colour.
Any treatment of a stone should be disclosed at the time of sale, however, with some treatments it is hard to know whether they have been carried out on a particular stone. Independent jewellers usually buy only from trusted sources so they can trust that the stones they use have only been treated in disclosed manners.
Sapphire Rings and Jewellery
Sapphires make excellent stones for all types of jewellery, including rings, because they are both tough and hard, and do not chip or break easily. They are most commonly set in 9ct or 18ct gold, although jewellers will set them in sterling silver upon request. Blue sapphires are usually available in many different settings over the counter, and fancy sapphires are often made up into commissioned jewellery at the customer’s request.