Sapphire - Information and Sapphire Jewellery Buyers Guide
Sapphires
Sapphires with their captivating colour have been prized for centuries and are one of the four 'precious' gemstones. They are found in several locations around the world with some of the best examples coming from modern day Sri Lanka. Sapphires are synonymous with their strong blue colour, but also come in many other tones, and are one of the most diverse gemstones.
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The Formation of Natural Sapphire:
Sapphires are formed over millions of years in the earth by pressure and heat in areas rich in aluminium. Sapphires are made from corundum (aluminium oxide), if that sounds familiar to diy enthusiasts you are quire right, they are made of the same chemical composition as aluminium oxide used in sandpaper. Sapphires take on a blue colour due to the presence of minute amounts of titanium and iron, when they are formed, but sapphires also come in other colours. Sapphires occur naturally in green, grey, black, yellow, purple and orange along with blue. They also come in red, but we call these rubies - ruby and sapphire are basically the same (corundum) with different trace elements causing the colour difference.
Sapphires in Jewellery
Sapphires are second only to diamonds in hardness so make an excellent choice for jewellery which will be worn regularly such as engagement rings. Sapphires are very resistant to most household chemicals although it is suggested to avoid bleaches and harsh abrasives. Some sapphires can be fracture filled and the fillers used are not as tough so may be harmed more easily. Sapphires can be chipped, so it is best to remove your jewellery if you are undertaking rough manual work.
Sapphire Value
Colour has the greatest effect on sapphire value, for blue stones strong saturation and a velvet to violet blue are most desirable. Darker or lighter stones are generally less valuable as are those with obvious colour zoning.
Clarity is also important. Most sapphires have some inclusions with fine needles (called silks) being most common. The clearer the stone the more valuable, aside from some examples from Kashmir where the tiny inclusions give a sought after visual appeal.
Cut - the 'cut' of a sapphire in relation to quality depends on a number of factors much like for diamond. Factors include the proportion, shape, and quality quality of surface polish
Carat - the carat of a sapphire is simply it's weight with the unit being a 'carat'. One carat is 200 milligrams metric weight and for gemmology and jewellery purposes a carat is also divided into 'points'. One carat = 100 points, so a 20 point sapphire is 1/5 carat for example.
If you can measure the sapphire then you can use a mathematical formula to estimate its weight, although this is never quite perfect as slight differences in the facets and cut will skew the result. If the sapphire is not mounted in jewellery it can be weighed on specialist scales for a near perfect result. When set in jewellery carat weights are estimated within the limits of accurate measurement.
Sapphire Certification
Sapphires can be tested and certified by specialist laboratories, perhaps the best well known being the GIA. Gems are tested by specialists using advanced tools to certify their quality, their origin (natural or synthetic), and any treatments or enhancements they have received.
These tests are best done on unmounted stones before they are set into jewellery, and a certificate from a respected laboratory will increase the value of the gem. However such testing is not cheap with prices currently around £120-250 ($150-300) for a comprehensive certification. While worthwhile for higher value pieces for everyday jewellery it is generally not done as it significantly increases the cost for little benefit to the consumer.
It is important to note that mounted sapphires cannot be tested to the same standard and only certain criteria can be checked, results will also be less accurate. Also note that there are many labs (especially labs in India and China) which provide credit card type certificates with stones. The value of these certificates is limited and cannot be relied upon for accuracy and they are sometimes more of a marketing exercise than an impartial test.
Sapphire Enhancements
Natural sapphires are often subjected to 'enhancements'. These are usually designed to reduce visible flaws, improve the colour or stabilise faults. Some of these techniques are difficult to detect in the secondary market without advanced (and expensive) tests. A GIA certification should reveal such treatments but will lead to a significant increase in price for the item.
Common enhancements include:
Heating: Heat treatment of sapphires is routine and seen as acceptable in the gem market, so much so that all sapphires should be considered heat treated unless there is evidence to the contrary. It is done to enhance the colour and clarity and is a permanent treatment that does not degrade over time nor cause harm to the gem. Heat treatment can sometimes be detected using a good quality loupe or microscope. A professional lab should be able to determine if a sapphire has had heat treatments.
Fracture Filling: Using specialist types of glass or silicones to fill in natural fractures and faults within the sapphire. There are a number of techniques and processes used and this type of treatment is generally applied to larger stones. Fracture filling can often be detected under the microscope, although this may be much harder on mounted gems.
Backings: Some antique sapphires set in jewellery would have a metal foil coating applied to the backs to enhance their sparkle, this process is not considered detractive and can be a good confirmation of antique origin and increase the value of the jewellery.
Lab Grown (Synthetic) Sapphires
Lab grown corundum (sapphire and ruby) was developed in the late 19th century with Auguste Verneuil being the most influential in making the method commercially viable. The first retail stones came onto the market around 1905, well over a hundred years ago.
There are two main processes for the production of synthetic corundum, flame fusion and hydro thermal, with the former being the most popular. Lab grown sapphires have the same chemical make up as natural gems and will test as sapphire. Generally they can be distinguished from their natural counterparts by optical analysis under the microscope.
Lab grown sapphires allow the buyer to have a larger stone of far superior clarity and colour compared to a natural example at a lower cost. They are increasingly popular as they do not carry the concern of societal issues in the countries where natural sapphires are mined. They also avoid the need for mining which can have environmental issues, although it should be noted that production does still require significant amounts of energy.
Sapphire Simulants
Simulated sapphires are not genuine sapphires, but alternative gems which have a similar look. They can be man made or natural, but they will not test as sapphire and may have a lower value.
Common natural simulants include:
- Blue Spinel
- Blue Topaz
- Blue Quartz (caused by inclusions or dyeing)
Common man made simulants include
- Lab grown spinel
- Lab grown moissanite
- Lab grown quartz
- High dispersion glass (eg Swarovski Crystal)
- Cubic Zirconia (CZ)
As long as you understand what you are purchasing there is no problem with buying jewellery with lab grown or simulated sapphires at the appropriate price.