of them are sold as such mounted in brooches and different forms of jewellery.
The
artist may have used Vesuvian lava, or perhaps mother-of-pearl shell to
work upon, and there are many such cameos to be had. These lava gems,
if gems they may be called, range from a dirty cream colour to grey,
and almost black. They are easily distinguishable by their colour,
opacity, and softness. Of course, neither of these types are
imitations, but, on the contrary, may be genuine works of art, though
not necessarily of any great value. Many fine examples of cameo exist
that have been carved out of such a mineral as Steatite, a variety of
Talc, greenish or grey in colour, soft and very soapy to the touch, in
fact, the " soap-stone " of tailors.
The
Assyrians, Egyptians, and Greeks used Steatite, besides harder and less
perishable stones, such as the. Onyx and Carnelian. Steatite specimens
are much softer than the lava forms.
Paste
imitations of cameos may be detected by placing them in hot water. This
dissolves the cement, and the front separates from the back. Intaglios
are more difficult to detect, owing to the object being in one piece.
For
all glass imitations of semi-precious or precious stones, the test of
hardness is, perhaps, the best, for the hardest glass used in their
production can be easily scratched by an ordinary piece of flint,
whereas the glass will make no impression upon the flint. The specific
gravity is in nearly all cases, with the exception of the Sapphire,
considerably higher than that of the stone imitated. Optical
properties, such as "dichroism," or unequal absorption of certain light rays, also afford good tests, glass not
