Grinding the diamond
Posted February 1st, 2009 by admin
The stone to be ground is fixed in a holder or a revolving chuck, and this is rapidly turned while another diamond, fixed in a long “stick,” is pressed against it. The cutting, or grinding process, must be carried out with tools or machines in which diamond is the principal agent. The actual facets are ground on with a mill, or lap, revolving horizontally at approximately 2000 to 2500 times a minute. The mill is a disc of steel and lead alloy, or cast iron of a specially hard and porous nature, into which diamond paste has been ground. This paste is made by grinding boart in a mortar and mixing the minute grains with a fine oil.
Various forms of cutting which involve a varying number of facets are used, and these will be explained later, but the stone must be cut with regard to the individual grain of the specimen. The grinding wheel must therefore be applied perpendicularly to the direction of the grain. The round, “brilliant” cut is the most common, but there are a number of so-called fancy cuttings, such as marquise and baguette, which need great care. Many of these shapes accentuate flaws and color defects, so only fine material is used for such specimens.
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