somewhat
hollowed behind (fig. 19), to receive a piece of foil as well as to
lessen the depth of colour in very dark stones. Our figures represent
the simple cabochon (fig. 17), the double cabochon (fig. 18), the
hollowed (évidé) cabochon (fig. 19), and the flattened form
much used for opals, and called tallow-topped (fig. 20). The double
cabochon is usually cut with the base of lesser curvature than the
crown ; but with many stones a more brilliant play of coloured light
within the stone may be secured by reversing these proportions.
Although the cabochon form is almost essential to many precious stones,
and is useful to hide the poverty and flaws of others, and also is
convenient in the case of stones to be used in the decoration of vases
and other objects to be handled, yet it ought not to be allowed to
displace the various faceted forms. Doubtless there is a quiet beauty
and richness in a good cabochon ruby, sapphire, emerald, or jargoon,
but we lose some of the most striking characteristics of these gems
when we so cut them as not to admit of the display of their dichroism,
and their dispersive and reflective powers. The narrow view that all
faceted stones are vulgar is based on caprice and ignorance ; it is the
mere unintelligent whim of a clique of artists and amateur writers on
art. For the faceting of the great majority of transparent stones is an
operation necessary for the development of those optical qualities upon
which the beauty of precious stones mainly depends. It should be
performed in strict accordance with certain rules of proportion, which
may be deduced from the optical constants of each species of stone.
Information
as to the mechanical processes and the materials employed in the
cutting and polishing of precious stones may be found in the works of
Jannettaz and Dieulafait. Horizontal wheels of steel, gun-metal,
copper, lead, pewter, tin and wood
