It is said that blue is the favourite colour of more than half the world’s population. Blue represents loyalty and friendship, harmony and sympathy – all important feelings in a relationship. This is why the sapphire is one of the most popular stones in an engagement ring. The sapphire symbolises loyalty and is also an expression of love and longing.
Sapphires belong to the mineral family corundum, the same family as the ruby. Corundum gemstones formed over many centuries when pure aluminium oxide was crystallised by pressure and heat deep below the earth’s crust. Different elements are responsible for colouring the stones. The ruby owes its red colour to the presence of chromium.
Sapphire Colours
As the name ruby is used for red corundum gemstones, so sapphire applies to all blue corundum gemstones. Sapphires in other colours are known as “fancies”, and referred to by the gemstone name prefixed with a description of their colour.
Clear sapphires are rare, because there is usually some element present that causes colourisation in the gemstone. Yellow and green sapphires owe their colour to the presence of iron. Pink sapphires and the rare purple sapphires derive their hue from vanadium. Brown, grey and black sapphires are also available.
The most valuable sapphire colour is “cornflower blue”, described as a deep, vivid and velvety blue with subtle violet undertones. Stones exhibiting this colour are known as Cornflower Blue Sapphires or Kashmir Sapphire, named for the magnificent stones exposed in Kashmir after a landslide in 1880. The colour of Kashmir sapphires is intensified by a silken shine, and the gemstones retain their hue in both natural and artificial light.
Special Sapphires
The rare padparadscha sapphire is highly prized for its subtle orange hue, blended with soft pink undertones. The name originates from the Sinhalese word for “lotus blossom”. Like the ruby, padparadscha sapphires are the only corundum gemstones to be given their own name. An untreated salmon-coloured padparadscha sapphire can be more valuable than a cornflower blue sapphire.
Star sapphires are another rare sapphire, displaying a star-like effect known as asterism. These gemstones contain needle-like inclusions that reveal a six-rayed star shaped effect when the stone is moved underneath a single overhead light source. Star sapphires are valued according to their carat weight and the quality of the asterism.
Colour change sapphires display different colours according to the light source. In natural sunlight they appear blue, changing to purple under artificial indoor lighting. Some colour change sapphires are pink in natural light and green under fluorescent light. Some stones change colour completely, while others only partially – from blue to bluish purple.
Grading Sapphires
When grading gemstones gemmologists refer to the Four Cs of Connoisseurship: Colour, Cut, Clarity and Crystal. Colour considers a stone’s hue, saturation and tone. Cut describes the percentage of brilliance in the stone when viewed face up as well as its proportions - length, depth and width. Clarity defines a gemstone’s inclusions or flaws, which add to a stone’s value when used for identification purposes. Inclusions are only called flaws when their presence negatively affects a gemstone’s beauty and durability. Crystal refers to the stone’s transparency; a good, well cut stone will appear to glow.
On the Mohs Scale of Hardness the sapphire is rated nine, making it the second hardest gemstone after the diamond, which registers ten.A sapphire’s value depends on its size, colour and transparency. For top quality gemstones the origin of the sapphire is also an important criterion.
Sapphires from Kashmir and Burma possess a deep blue colour, but today these gemstones are extremely rare. Sri Lanka and Madagascar are the biggest producers of quality blue sapphires, with colours ranging from light sky blue to dark blue. The rare purple sapphire is found in Tanzania and Sri Lanka. Sapphires are mined in Australia, Brazil, Cambodia, India, Thailand, Vietnam and the US state of Montana.
Common Sapphire Treatments
Many gemstones are heat treated to enhance and improve their hue, so sapphires that are guaranteed untreated are more sought after. A reputable jeweller or merchant will always advise if a stone has been treated. Heat treatment is commonly used for sapphires, to enhance a stone’s colour. Stones are subjected to heat of between 500° Celsius and 1,800 ° Celsius (932° Fahrenheit and 3,272° Fahrenheit) several hours prior to cutting. Care should always be exercise when heat treating sapphires, because the process can cause the gemstone to loose its “silk” effect.
Diffusion treatments are controversial because they add elements to the sapphire to improve the colour. The usual practice is to diffuse beryllium into a sapphire at a heat just below the stone’s melting point. The value of diffusion-treated sapphires is much lower than that of a heat-treated or natural gem. Surface diffusion is generally considered unacceptable, because this process can remove the coloured layer of padparadascha sapphires. Treated padparadschas can be difficult to detect, which is why anyone intending to buy one of these stones should obtain a certificate from a reputable gemmologist.
Caring for a Sapphire
The sapphire’s hardness makes it easy to care for. A sapphire ring can withstand daily wear and tear, and can be easily cleaned at home by soaking it in warm soapy water and using a brush with medium bristles on the setting. Avoid contract with solvents and harsh chemicals which can damage gemstones.
For further information please see The Mythology of the Sapphire.
Some fine examples of sapphires may be found at The Star Ruby Shop.
Sarah Todd - Born and brought up in Zimbabwe, I have been writing since I was at school. For ten years I worked at a public relations consultancy, and ...
