HEAT TREATMENT OF SAPPHIRE
( A layman's simplified
explanation of the various levels of treatment)
Sapphire is formed deep down
below the earth's surface, some 65 kilometres down, and comes to
the surface in a volcanic explosion in a 'formation tube' or
vent. The sapphire comes up at the forefront of a volcanic
eruption and is expelled with the pyroclast, or volcanic ash.
This is typical for all Australian sapphire occurrences.
If the temperature in this
formation tube is hot enough, and the residence time is long
enough, the sapphire is clarified, on its journey to the
surface. The main contaminant in sapphire is rutile (Iron -
Titanium Oxide) and if the temperature/time relationship is
sufficient this is volatilised and expelled from the sapphire or
it is reabsorbed add reconverted within the crystal.
However, if the temperature is
too low, or the rate of travel of the sapphire and pyroclast up
the tube too rapid, the sapphire may be left with inclusions
such as the "silk" veils which often cloud natural sapphire
The Thais developed the
practice of commercial heat treatment many years ago to remove
these silk veils to produce stones of improved clarity and
brilliance This process has always been considered quite
acceptable as no chemicals were added, and the holding of the
sapphire at high temperatures to bring about this improvement
was essentially only mimicking nature and was just finishing off
what nature had started.
However, the heat treatment
technology has been greatly extended in man's quest to turn
lower quality material into brighter stone in the endless search
for more profit - and some quite dubious if not actually false
practices have resulted in recent years!!
A simplified explanation of the
levels of heat treatment is as follows :-
a. Natural Untreated
This may be totally clear or
may have small inclusions or silk bands. Whilst it was once the
accepted practice to heat treat to remove all "silk', this is
now not always done as a small quantity of silk is considered
acceptable, if not actually desirable since untreated good
quality material usually commands a premium price. We try not to
heat treat wherever possible.
b. Simple Heat Treatment
This is considered quite
acceptable in the jewellery trade as no chemicals are added and
the sapphire is not changed chemically apart from the removal or
conversion of the rutile and contaminant bonds.
This is a simple process
brought about by a one-off heat treatment, and the resultant
clarification of the sapphire is permanent and irreversible.
No radiation, chemicals or
health risks are involved in this process.
EVERY SAPPHIRE WHICH ORIGINATES
FROM THAILAND OR IS CUT IN THAILAND MUST BE CONSIDERED TO HAVE
BEEN SUBJECT TO AT LEAST THIS SIMPLE HEAT TREATMENT AS NORMAL
c. Multiple Heat Treatment -
In certain cases, the amount of
included material is too great to be removed by the simple
one-off heat treatment process, So a system was developed of
multiple heat treatments, sometimes in the presence of fluxing
agents, which eventually lead to a clearer or brighter stone of
Much of the "Ceylon" sapphire
on the market comes from Australia or from Madagascar and may
have been subject to a simple treatment process, but a portion
of it started off life as Geuda Stone from Sri Lanka. This very
highly included stone looks like a "moldy potato" before heat
The geuda stone is heat treated
as many as six or eight times in order to clarify it and produce
the pale "Ceylon Blue" which is sold at quite high prices - but
is essentially a heat generated colour.
d. Bulk Chemical Diffusion -
The chemical diffusion process
is carried out by multiple heat treatments of the sapphire in
the presence of artificially introduced elements like beryllium
or titanium, which penetrate the structure of the sapphire.
The beryllium treatment is
carried out to produce golden, yellow, orange, apricot,
padparadschas and similar colours from lower grade rough
sapphire or from sapphire of less desirable colours. The
beryllium can penetrate the sapphire to a considerable depth and
can be difficult to detect.
The chemically modified stone
may have good colour and brilliance, but it is no longer a
'natural sapphire' and cannot be sold without proper and
adequate disclosure of the treatment it has suffered. It is
essentially a "fake", albeit sometimes a very good one!!
The titanium treatment is
carried out to enhance the colour and brilliance of blue
sapphires, but the depth of penetration is far less than that
for beryllium treatment and consequently repolishing of a stone
may remove part of the chemically imparted colour.
Concerns have been raised as to
the possible health risks arising from the beryllium treatment
process, and these concerns are very real for the operators of
heat treatment furnaces as the beryllium vapour is highly toxic.
Beryllium treated sapphire has
only been present on the world markets - in the last two years
or so, and it is still too soon to know whether the process may
result in any long term health problems for the wearer of such
chemically treated stones.
Persons selling beryllium
treated sapphires are required to disclose the fact clearly and
adequately to purchasers. However, since some sellers have been
known not to make the requited disclosure, buyers are
recommended to seek a guarantee or statement of authenticity for
Anybody who wishes to gain more
technically correct or detailed information on the treatment
process can do so by visiting the website of Gemlab Inc., whose
principal, Mr. Ted Themelis has been a world leader in such
technology testing. His website is
Coolamon Mining Pty. Ltd
guarantees that no chemical treatment of any kind is used in the
production of our sapphires, and that all information is
The above article was
extracted from a talk given by Mr. Jim Elliot, Coolamon Mining,
at the Central Queensland GEMFEST - August 2003
genuine sapphire -
made by nature
Resource on the Australian Sapphire Industry