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 Treatment |
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 Various techniques |
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 There are various techniques of
modifications intended to improve the appearance of precious stones, namely: |
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 Traditional treatments: the heat
treatment of the corundums (rubies and sapphires) and colourless
oiling of emeralds are practised since several hundred years. They are
« tolerated » treatments. |
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Recent treatments, known as specific, by
diffusion, irridiation, bombardment, coloured oiling,
filling by resins, high pressure/high temperature, result from the new techniques of
development. They must be obligatorily mentioned to the client. |
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| Concerning rubies and sapphires |
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Heat treatment will
improve the depth of colour because heat causes dissolution of inclusions and
diffusion of impurites (especially Ti from rutile inclusions) into the
surrounding corundum. Because fine inclusions cause some stones to look
cloudy, heat treatment that dissolves the inclusions may also improve the
clarity of the stone. |
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Heat treatment may also
remove local colour concentrations (remove patches of colour) because heat
allows the colour-causing impurity (Cr, in the case of ruby) to more evenly
distribute through the crystal. (however, this may require such long times
that it is impractical). |
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Diffusion is a means of
changing the colour of a gemstone by heating under pressure in a particular
chemical environment (generally, a gas enriched in a particular element).
Historically, this produced a colour change confined to a shallow region near
the surface of the stone. Consequently, chips or scratches could sometimes
expose the original colour of the stone. |
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| Concerning emeralds |
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Nearly all natural
emeralds have extensive internal flaws. The appearance of these stones is
markedly enhanced by first, placing them in a vacuum chamber and then
immersing them in cedarwood oil (or another colourless oil). When the vacuum
is removed, the oil is pulled into the minute spaces between fracture planes,
making them less visually apparent. |
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This treatment can
produce a remarkable change in the appearance of an emerald, greatly
enhancing the beauty and clarity of the stone. |
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In recent years, several alternative
filling materials have come to market. The most famous is « Opticon ». Opticon
and other epoxy resins are used in conjunction with hardeners. |
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| Concerning diamonds |
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Clarity enhanced:
diamonds are occasionally laser drilled to eliminate dark inclusions.
Occasionally some diamonds are fracture filled with a foreign substance,
which has good stability except during repair. Fracture filled is the process
by which a substance of the same optical density as that of a
gemstone is pressure filled into a fracture of that gemstone.
These diamonds are called clarity enhanced and must be disclosed.
Irridiation: irradiation of diamonds has been around for a long time
and uses a nuclear reactor or linear accelerator to create fancy coloured
stones. These are generally over coloured and then annealed or heated to
soften the shade back to a desirable and permanent colour. Such treatments
need to be disclosed by merchants/vendors as well as labs, it is illegal not
to.
HPHT process: this process, using a high pressure/high
temperature process (HPHT), changes inexpensively brown diamonds into near
colourless white diamonds worth more than twice as much. |
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1.72 carat H-VVS1 |
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1.57 carat D-IF |
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1.58 carat E-IF |
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0.45 carat D-SI1 |
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1.99 carat H-VVS2 |
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| Price: £ 10,183 |
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| Price: £ 34,366 |
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| Price: £ 26,831 |
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| Price: £ 771 |
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| Price: £ 11,316 |
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