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PRECIOUS STONES.
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cutters,
though as a rule the full number of facets are not worked on them.
Specimens which are too thin to be cut as brilliants are rose-cut, and
very thin cleavage slices are often polished on the two parallel
surfaces and used as a cover for miniatures.
Brilliants
are almost always mounted now in an open setting, or set " a jour ";
that is, they are held by a series of metallic prongs, projecting
towards the girdle. These prongs are notched at the end, and one part
goes above the girdle and the other below, thus firmly holding the
stone and leaving the culasse exposed. Previously Diamonds were always
set in a closed setting, completely covering the culasse; and this
portion of the stone was covered with a " tincture," a varnish made of
mastic, coloured with ivory black, which was supposed to add to the
beauty of the gem. A stone showing darker patches is sometimes mounted
in a closed setting, and this varnish applied so as to come below the
lighter portion; thus the stone will seem of more uniform appearance.
This is known as " mounting on moor."
Rose-cut stones are always mounted in a closed setting.
Value.
Of
the value of Diamonds it is difficult to speak with any precision, as
so much depends on the quality of the stones, and in the case of large
stones, which very few people could afford to buy, so much depends on
whether any such people wish to buy at that time. The old rule of
Tavernier to find the value of a given Diamond, cut as a brilliant and
of the finest quality, was to square its weight in carats, and multiply
by eight. Hence a stone of two carats was worth
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