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are
used. Heat treatment has also been found to improve the colour of
streaky rubies and some amethysts. The following stones on heat
treatment give the colours noted against them.
Greenish beryl—bluish colour appreciated in
aquamarine. Dark blue tourmaline—pleasing green of emerald. Dark green stones turn to lighter shades.
3. Heat and pressure.—Pressed
amber or amberoid is an example. Small pieces of amber are selected
according to colour, all the impurities are removed and heated to
200-250°C. with exclusion of air. It becomes soft and could be moulded
to desired shape. After cooling it hardens when it is easily finished
and worked for the market.
4. Radium treatment.—Gem-stones
are also liable to some change of colour when treated under radium
emanation. Colourless diamond after long treatment becomes green.
Colourless and rose quartz are turned smoky brown, and the colour of
decolorized amethyst may be restored. The changes caused by radium have
not much practical application.
5. Special mountings.—The colour of a stone could also be improved by mounting stones over foils or coloured enamels.
SYNTHETIC
GEMS. Synthetic gems resemble very much the natural stones as they have
the same chemical constitution. They are also sometimes called
'scientific stones' but this term refers also to imitations. But the
synthetic ruby and natural ruby consist of Al20s, and have
the same physical properties as regards hardness, specific gravity,
cleavage, refractive index and so on. But certain incidental and
characteristic features are found helpful in the identification of
synthetic stones and differentiating them from natural stones.
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