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The technique developed in the early 20th century for dividing a rough diamond before bruting and faceting, instead of the former method of splitting according to the cleavage of the stone. The process of sawing in general divides the octahedral stone against its grain and along its 'sawing grain', preferably near its greatest width, resulting in two unequal stones each suitable for making a brilliant. The result is to require less bruting and to reduce the loss of weight.
It involves fastening the stone in steel catches on a sawing machine and keeping it against the sharp edge of an extremely thin disc of phosphorized bronze that turns vertically, charged with a mixture of olive oil and diamond-powder. The duration of the operation may vary from a few hours to a few days, depending on the size and characteristics of the stone.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson