34 The Engraving and Carving of Precious Stones.
artist
naturally does not care to expend his time and talent on a stone which
will not display his work to the best advantage, and at its full worth.
For
Cameos it is desirable to select large stones, remarkable for beauty of
colour, with different layers or strata ; although choice works of art
have sometimes been elaborated on gems of only one colour.
The
greater the number of layers that an Australian Opal or an Onyx or
Sardonyx has, and the more beautiful and varied the colours which it
presents, the more costly is the stone. The best stones for this
particular work are those with a white layer on a dark ground. They are
still better where there is a third layer above, such as white with a
reddish or brownish tinge, which the artist can work into hair,
wreaths, or dress. Entirely transparent Stones are very rarely used for
Cameos.
Stone
engraving is said to have been introduced into the West by Jews from
Alexandria. In the Middle Ages and even in later times, when there was
no great master in the Art of Engraving, the cut stones of the ancient
Greeks and Romans were used as signet rings. King Pepin sealed with the
Indian Bacchus, and Charlemagne with a stone representing Jupiter
Serapis.
Later
on, signet rings were engraved with the king's signature; and lovers
were wont to exchange at their betrothal, rings cut to represent wishes
or allegories.
In
the fifteenth century, when Constantinople fell under the dominion of
the Turk, the Greek artists left their fatherland, carrying with them
into Italy their secret knowledge of stone engraving. The first fruits
of this immigration were seen during the Pontificates of Martin V. and
Paul II. Lorenzo de' Medici assisted the development of the art by
affording to Giovanni Bernardi the means of
