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CRYSTALLUS.
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comes
an imitation of the Emerald. Crystal may also be coloured by the dry
method, by placing the pieces upon orpiment and arsenic mixed together
in a crucible, and so exposing them to heat. The cold method consists
in steeping the Crystal in oil of turpentine saturated with verdigris,
or spirits of wine holding dragon's blood or other coloured resins in
solution, the depth of tint produced being proportioned to the time of
steeping. Such false Eubies are still known to the French lapidaries
according to Barbot by the name of Rubaces. In London they
figure as " Rubies of Ancona." But the substance of the Crystal is not
really coloured ; it is merely the dye, which, insinuating itself into
the innumerable minute fissures produced by the sudden cooling, that
apparently stains the entire mass ; and the great art in the process is
so to regulate the heat that these fissures be not too apparent upon
the surface of the imitative gem.
It
is, however, not unlikely that the ancients employed also the more
simple method now so much in use, and which produces most of the
Carbuncles seen in the London shops, viz., after cutting the Crystal
into shape, then to paint the reverse with the required colour, and so
to set it with a backing. The fact that anciently gems were for the
most part set in such a manner would greatly favour the execution of
this fraud, to baffle which Pliny expressly notices that the better·
kinds of Jaspis and Chrysolithus were mounted à jour, " funda
perspicua." Although the Roman jewellers made up the false Sardonyx of
three layers by cementing together as many slices of different coloured
stones, yet they do not seem to have been acquainted with Doublets, that
favourite device with the modern trade, in which a thin slice of the
true gem, improved by cementing a paste of the proper colour
underneath, assumes the appearance of a first-class stone in its
(G)
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