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PRECIOUS STONES.
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may
be clone in half an hour by carefully boiling in pure olive oil and
then, after drying, putting them into the acid. If they become too
black, their original colour may be restored, or, in other words, the
blackness may be removed by warming in pure nitric acid. A solution of
sugar may be substituted for oil.
"
Off-colour" or yellowDiamonds, known as " straws," have been passed off
by unscrupulous dealers as "first water" stones by dyeing them with a
magenta varnish, which neutralises the colour. This in time wears off
and their true colour shows up. Soaking a suspected stone in absolute
alcohol for a moment, and wiping, will soon remove any varnish if there
be any to remove.
A
method of fraud very little practised, perhaps, because it entails no
little skill and the use of real stones, is the production of "
doublets " and "' triplets."
A
Diamond or Sapphire, more often the latter, that, owing to shape or the
number of flaws it contained, would be useless for cutting as a
brilliant, is cut as half a one, i.e., the upper or table
portion. This portion is then ground perfectly flat at the back and
cemented by means of a clear transparent cement to the lower or collet
half, cut from either Sapphire or paste as the case may be. Such a
stone when clasped is difficult to detect, but on being removed from
the setting and placed in warm water, the cement is dissolved, and the
two portions fall apart much the same as when dealing with imitation
cameos.
Coloured
stones imitated by the above process have a thin slice of real stone
set between the two halves, or the cement used may be coloured. It is
to specimens set up in the former method that the term "triplet" is
applied.
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