Page:A treatise on diamonds and precious stones including their history Natural and commercial.djvu/175

 ness, is performed by a horizontal mill of thin iron, properly hammered, on the edge of which diamond powder is placed, and pressed into it so as to form teeth. Some nicety is required in corning the mill. The best method is to put half a grain of diamond powder in a watch glass, with a few drops of oil, and, with the point of a pen, to place a minute quantity ona small circular instrument, called a Gigger, which is then held against the edge of the mill, while itis gently turned round. By this means the diamond powder is equally distributed. Practical lapidaries usually put a small quantity of powder on a block of steel or a smooth stone, with a drop of oil, and rub it with a muller to separate the particles; they then apply it to the mill with the finger, and set it in the edge by holding a piece of glass against it, at the same time turning the mill round gently.