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Gemstones

Articles from GEMSTONES - SAPPHIRE (12 Articles)












Figure 1. Natural, BeHT sapphire.  Figure 2. Synthetic, flame fusion sapphire
Figure 1. Natural, BeHT sapphire. Figure 2. Synthetic, flame fusion sapphire

Understanding inclusions: part 2 sapphire

Inclusions are an integral part of identifying any range of treatments that can be applied to gemstones to boost value. JUNE MACKENZIE reports.

If diamonds are a girl’s best friend then inclusions are surely a gemmologist’s best friend. Taking sapphires as an example, inclusions determine whether a gemstone is natural, natural but heat-treated, natural but beryllium heat-treated (BeHT) or synthetic.

Although there are synthetic flux sapphires and synthetic hydrothermal sapphires on the market, generally the favoured synthetic used in the trade is flame fusion, also known as Verneuil and named after the man who invented it. This is also the cheapest. While there are gemmological tests to determine what type of sapphire is being tested, a 10X loupe or microscope with higher magnification enhancing the inclusions usually provides confirmation.

Sapphires may undergo more than one treatment. One mine-run (batch) of gemstones may undergo many different treatments, making it difficult for anyone who has not been involved with the processes to be able to determine the type of treatments and how many have been undertaken.

A natural sapphire showing liquid films proves that the gemstone has not been heated or treated as these films would disperse or explode upon any type of treatment. A sapphire containing iridescent ‘silk’ of rutile needles, some with ‘arrow twins’ in a nest, also proves lack of heat-treatment.

A natural sapphire that has been heat-treated may show various tell-tale signs, such as long rutile needles that have been damaged and become lines of tiny particles. Discoid fractures may also be present. These are generally roundish and shiny or mirror-like in appearance with little sign of healing.

Depending on the heat, crystals within the sapphire may be damaged to varying degrees as different crystals have different melting points. For example, rutile has a melting point of 1,600 degrees Celsius, zircon of 1,855 degrees Celsius and corundum of 2,030 degrees Celsius to 2,050 degrees Celsius.

BeHT sapphires often change colour; they may have been blue or greenish-blue and change to orange after treatment as demonstrated by the Songean sapphire (Figure 1). Depending on the period of time that a sapphire is exposed to heat during the beryllium treatment, the colour may not completely diffuse into the gemstone but a different coloured rim from the colour in the centre of the gemstone may be visible when immersed in liquid. Blue, circular inclusions may be present as well as flux droplets.

Synthetic, flame fusion sapphires may contain bubbles, undissolved nutrient and curved striae. Some may show streaks of tiny bubbles known as brush strokes, which also confirm their identity (Figure 2).

These examples indicate the importance of inspection of a gemstone to indicate its status as natural, treated or synthetic – invaluable information for gemmologists and jewellers.

Retailers need to be aware that some treatments greatly affect the price of a gemstone. In addition, the Australian Competition and Consumer Commission (ACCC) states that businesses in Australia must be able to guarantee what they sell. If gemstones are treated, then this must be disclosed to the customer and written on their receipt. To finish, never forget that inclusions can also tell a wonderful story about gemstones.












ABOUT THE AUTHOR
June Mackenzie

Contributor •


June Mackenzie FGAA Dip DT, is a qualified gemmologist and gemmology teacher in NSW. She is the developer and presenter of the GAA Advanced Gemstone Inclusions course. For more information, visit: gem.org.au









Saturday, 18 November, 2017 10:56pm
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