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PRECIOUS STONES. 57
hand.
In the case of the Diamond, unless the rough stone is of the octahedral
form already, cleavage is first made use of as far as possible. In
cleaving a Diamond the stone is cemented firmly to the end of a support
in such a position that when the support is fixed on the bench so as to
be vertical, the cleavage plane to be attacked will also be vertical.
The support is then put in position, and means taken for ensuring the
collection of any fragments. A steel blade is now placed in the
cleavage plane at the desired point and a sharp tap delivered on the
blade by a rod held in the right hand; by repeating this process a
cleavage octahedron free from flaws is produced. The cement used is a
solution of shellac in turpentine, thickened with very fine brick-dust.
Often before applying the cleaving blade a fine groove is cut in the "
trace " of the cleavage plane by means of another Diamond. The art of
cleaving Diamond is said to have been known in the East from ancient
times ; it seems to have been discovered independently by Wollaston,
although De Boot (1609), speaking of the Diamond, says he knew a
physician who could, "without the aid of any instrument or material,
other than those furnished by the human body, divide it into fine
scales like a piece of talc." However, Dr. Wollaston turned his
discovery to good advantage by buying up mis-shapen Diamonds that the
jewellers had considered not worth the enormous labour of grinding into
shape, and, by cleaving them, he reduced them to a form easily worked
on.
After
the cleaving has been effected by one workman, the stone is handed to
another, who is known as a bruter. Tbe operation he performs is the brutage, or bruting. This operation is the outcome of de Berquem's discovery
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