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: In the new beryllium diffusion process, the gemstones are
heated for 100 hours at 1780oC in an oxygen rich atmosphere with a little beryllium.
In the first of two methods, between two and four per cent chrysoberyl powerder
is added to borate and phosphate fluxes. This method only diffuses the colour
a little way below the surfase of the stone. In the second method, the chrysoberyl
power is added to high purity aluminium oxide (sapphire) powder. The powder method
diffuses the coour all the way through the stone. Sometimes, chrysoberyl powder
is replaced with high purity beryllium oxide powder and this enables a reduction
in process time to 36 hours.
This process produces the complete range
of known gemstone colour plus a few ore that are unique. The low concentration
of beryllium renders it undetectable by most analytical instrument.
unprocessed Montana sapphires and pale yellows from Madagascar turn yellow or
orange. Some very pale yellows from Madagascar and the bluish and greenish stones
from Songea turn bright yellow or golden. The 'colourless' Sri Lanka sapphire
which result from heat treating certain type of geuda also becomes yellow, gold
or orange. In some ofhte greenish-yellow Australian sapphires from the Subera
deposit the greenish overtones are removed and the stones become good yellows
or golden. The proces also works on high purity, colourless synthetic sapphires
like the Czochralski -grown ones produced by the Union Carbide corporation. They
develop a golden yellow colour.
Many of the rubies from Songea and Madagascar
have a strong bluish hue component which is replaced with yellow and the stone
become a strong orange when diffused completely. However if the diffusion is limited
to a surface layer, the yellow surface layer will visually cancel out or offset
the blush core and give rise to a very good ruby colour. These stone can of course
be relatively easily detected. However, by completely diffusing the stone so that
it turns ornge and then subjecting it to simple heat treatmet the yellow overtone
is removed and an optimal ruby colour is achieved.
The same two-step
full diffusion and heat treatment can be used with pink sapphires to achieve padparadscha
orange without a visible diffusion layer. Stones produced by this two-step method
are very difficult to detect.