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72
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PRECIOUS STONES
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with
such success as occasionally to deceive all but experts. Such
imitations are costly, though, of course, not approaching the value of
the real stones : it being no uncommon thing for valuable jewels to be
duplicated in paste, whilst the originals are kept in the strong room
of a bank or safe-deposit.
In
all cases, however, a hard file will abraid the surface of the false
stone. In chapter VII. we found that quartz is in the seventh degree of
hardness, and an ordinary file is but a shade harder than this, so
that almost all stones higher than Xo. 7 are unaffected by a file
unless it is used roughly, so as to break a sharp edge. In order to
prepare artificial diamonds and other stones for the file and various
tests, they are often what is called " converted " into " doublets " or
" triplets." These are made as follows : the body of the glass is of
paste, and on the " table " (see last chapter), and perhaps on the
broader facets, there will be placed a very thin slab of the real
stone, attached by cement. In the case of the diamond, the body is
clear, but in the coloured imitations the paste portion is made
somewhat lighter in shade than the real stone would be, the portion
below the girdle being coloured chemically, or mounted in a coloured
backing. Such a stone will, of course, stand most tests, for the parts
usually tested are genuine.
A
stone of this nature is called a " doublet," and it is evident that
when it is tested on the underside, it will prove too soft, therefore
the " triplet" has been introduced. This is exactly on the lines of
the doublet, except that the collet and perhaps the pavilions are
covered also, so that the girdle, which is generally en-
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