used for gem-stones. The term grain is also in use. A pearl grain is 1/24 of the gram.
In India rati was used. Rati = weight of 1 seed of Abrus precatorius = 1/2 a carat, but it used to vary. Now international carat is in use, i.e. 0.200 grams, from 1913. (Gemmologist, January, 1936.)
Chapter IX
SYNTHETIC AND MANUFACTURED. GEMS
SEVERAL
gems are very precious and expensive and most people may not be able to
go in for them. But it is natural for everyone to have a yearning to
own precious or semi-precious gems and for the poorer classes to have
some cheap jewellery. To cater to the varying buying capacities of
people the following materials are also available in the market: (a) treated gems, (b) synthetic gems, (c) imitation gems, and (d) doublets and triplets.
The
manufactured gems also include natural stones, whose qualities are
modified or improved by artificial means. Their value is actually
raised by such means. Those manufactured in the laboratory consist of
synthetic rubies, sapphires and spinel.
Treated gems.-—Some
stones are amenable to treatment, which increases their beauty and
value. The treatment consists of several methods, and the stones may be
subjected to the following processes: artificial colouring, heat
treatment, heat and pressure, radium treatment and special kind of
mounting.
1. Artificial colouring and staining.—Some
pale agates are improved by this process by soaking the agate in
suitable solutions. The different layers of agate possess varying
degrees of perviousness, which allows them to be coloured in various
shades with a pleasing contrast. The agate is immersed in a solution of
sugar or honey and then soaked
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