Jeweller - March Issue 2017

GEMS
REVEALING INCLUSIONS: SAPPHIRE
FIGURE 1. NATURAL, BEHT 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.
FIGURE 2. SYNTHETIC, FLAME FUSION SAPPHIRE
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.
A NATURAL
SAPPHIRE
SHOWING
LIQUID FILMS
PROVES THAT THE
GEMSTONE HAS
NOT BEEN HEATED
OR TREATED
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. i
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
March 2017 Jeweller 37