Sapphire – guide to the queen of gems
Sapphires have endured as one the key precious stones of choice for royalty and the well to do for many centuries but in more recent times they are becoming increasingly popular as the centre stone for engagement rings and bridal jewellery. As with all things luxury celebrity endorsement has helped this rising popularity, not least as a result of Prince William’s decision to propose to Katherine Middleton with an 18 carat blue sapphire that was once in the possession of his mother Diana, Princess of Wales. The ancient Persians of antiquity thought the earth itself rested on a giant sapphire, which accounted for the deep blue of the sky, and the early Christians believed the ten commandments were inscribed on a sapphire tablet that was so strong it would break a hammer if it was swung against it with full force! The etymology of the word sapphire is disputed but the most likely origin is in the Hebrew word “spir,” which is referenced in the Hebrew Bible when describing blue sapphires.
(Sapphires have been adored for centuries, most commonly blue, they can be found in any colour)
Sapphires are the non red variety of the mineral corundum (red corundum being a ruby) and they are most common in their blue form, although they can be found in a wide range of colours. Besides blue, these include pink, yellow, green, orange, brown and clear. Sapphire is the name given to a couple’s 45th wedding anniversary (the 40th belonging to her sister stone, the ruby) and it is the birthstone of the month of September. With a Mohs’ mineral hardness of 9 (on a scale of 1-10) they are second only to diamond (which hold the benchmark score of 10). Colour is the most important determiner of value with coloured gemstones, including sapphires. Colour is defined by hue, tone and saturation. A stone’s hue refers to the balance of colour in relation to its neighbours on the colour wheel and it is often measured as slight or strong. With blue sapphires the stronger and deeper the blue the more valuable the stone.
The most desirable are defined as “cornflower blue,” which take their name from the fact that the cornflower is almost unique among flowers because it’s petals are pure blue, as opposed to violet or purple (as is the case with most other ‘blue’ flowers). Tone refers to how light or dark the colour within the stone is, ranging from very light to very dark. Once again, the darker the stone the rarer and hence more expensive it becomes. Saturation relates to the vibrancy of the colour, covering a full spectrum from dull to pure vivid (with the finest appearance of colour). High saturation, vivid stones without elements of brown or gray areas, referred to as extinction, fetch the highest premium. Unlike diamonds, sapphires and all other coloured gemstones do not have a fully standardised system, which can make comparison between stones more complicated.
(A ‘Cornflower’ blue sapphire)
Experienced dealers and jewellers have an eye of the most sought after stones and their advice and guidance is crucial in achieving value for money. The Padparadscha Sapphire is a very rare pink-orange fancy sapphire from Sri Lanka and Myanmar (Burma) that can fetch over $25,000 USD per carat and it derides its name from the Sanskrit “padma raga,” meaning “lotus colour,” due to its resemblance to the lotus flower. The larger the chromium content of a corundum, the deeper the shade of pink it will become and (as covered in our earlier article A guide to buying rubies) the distinction between a pink sapphire and a ruby is not always clear cut although in some countries, including the United States, there are some guidelines.
Truly flawless sapphires are almost non-existent and in fact a stone with no inclusions will instantly arouse suspicion that it me be synthetic or heavily treated. All corundum contain rutile needles, known as ‘silk’ and, as with rubies, the vast majority of sapphires (some estimate over 90%) available today have been heat treated in some way shape or form. Due to the prevalence of inclusions in sapphires, it is “eye clean” stones that tend to be the more attainable, rather than “loupe clean.” As with rubies, some sapphires contain ‘asterisms,’ where light is reflected from the silk to form a ‘star’ shape, which can actually add value to the stone.
(Silk – rutile needles within a sapphire)
Unlike diamonds, there are no standardised cut for sapphires so in essence it is down to the cutter to produce the best possible shape to maximise a sapphire’s colour and clarity. As a rule of thumb however, a well polished sapphire will be symmetrical and it will reflect and refract light in the optimum angles to give the stone the best possible account of itself. With very light stones it is sometimes necessary to cut very deeply in order to accentuate it’s colour. With very dark stones the opposite is true and shallower incisions can produce the best results. In general the most desirable shapes are oval, round, cushion and emerald but a non faceted cut, such as a cabochon, can often do justice to a sapphire containing an asterism or double asterism.
(Asterism, or star, within a blue sapphire)
Gemstones differ widely in terms of their density, a fine emerald may be as much as 30% larger in terms of its dimensions versus a diamond. Sapphires are generally heavier than diamonds so a sapphire may appear slightly smaller than a diamond of the same carat. Consequently it is sometimes more useful to measure a sapphire in terms of its diameter in millimetres rather than its carat; a 1 carat sapphire generally measures around 6 mm. Always be mindful of the fact that the vast majority of sapphires have been heat treated in some way shape or form and as such it can prove difficult to determine a natural stone from a synthetic one. Above all else, it is essential to purchase a sapphire from a reputable source and ensure that its colour is as deep as possible.