Cleaving/Sawing
 
Cleaving is a method of splitting a diamond parallel to the direction of crystal grain with a single blow. It is done to divide the stone into two or more pieces, or in order to remove impurities or irregularities.

To cleave a rough stone, it is placed in a wooden holder in a quick drying glue. Another diamond, also placed in a holder, is used to make a nick on the marked line. A steel cleaver with a rounded edge is then placed into the nick. A sharp blow with a hammer splits the stone.

Sawing is a method of splitting a diamond against the grain of the crystal. In preparation for mechanical sawing, the diamond is set in a copper cap, with a paste consisting of a mixture of plaster and glue. When the paste dries, the cap is mounted on a sawing machine. An extremely thin disk, which is evenly smeared with a mixture of oil and diamond powder is used to saw the diamond. Its rotation speed varies from 15,000 to 17,000 revolutions per minutes, and at best the sawing of the diamond proceeds at 2 millimetres. Consequently, the sawing of a large stone can take days or even weeks.

A more modern method of sawing a diamond involves the use of lasers. While this entails a nominally higher loss of weight, the rate of production is significantly higher.
 
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