by
a hammer, at the same time moving the pestle about until the whole of
the fragments are completely crushed into an impalpable powder, which,
as well as the powder rubbed off in the cutting process previously
described, is (when burnt to remove the oil) of a grey colour, and is
worth from 16s. to 18.s. per carat.
Diamond Splitting.
The
splitting or cleavage of diamonds has a double purpose,—namely, the
removal of defective parts, fissures, or specks in the stone, and the
formation of facets in the rough. This operation is only applied to a
diamond when its natural form does not admit of its being cut in the
regular way without a great expenditure of time and labour. Stones of
a rhombic do-decahedral form are nearly round, and the cutting is
immensely shortened by splitting the facets from the rough; sometimes
"usable" pieces are split off.
The
workman must have an exact knowledge of the structure and cleavage of
the diamond, and as the form of the brilliant corresponds nearly with
that of the octahedron or dodecahedron, the natural direction of
cleavage much assists the lapidary. In order to split a diamond it is
fastened into a stick, the top of which contains cement, and the part
required to be split off is left uncovered; to avoid missing the proper
plane of cleavage, a line is scratched on the surface with another
diamond, to mark the exact
