Print representing a mill for cutting and polishing diamonds

This print shows the method of cutting and polishing diamonds in use in the middle of the eighteenth century. Little change has taken place in the method up to the present day.

The rough stone was cemented with mastic into a block of wood with a handle by which it was held, by means of a set screw, in a triangular frame so as to act as its third point of support. The lap was a soft steel disc on a vertical spindle with adjustable conical pivots. Three or more of these spindles were supported in a wooden framing with a table at the level of the lap. The spindles were rotated by gut bands from a wooden flywheel with a crank and connecting rod worked by a boy. Two legs of the frame rested on the table and the diamond rested on the lap which was fed with diamond dust mixed with olive oil. Pressure might be put on by loading the frame with leaden weights.