Diamond-dust may be bought in most large cities ready prepared. It is not a very costly article, as it is made of waste pieces obtained in cutting jewels, and a little of it lasts a long time.
Diamond-mills, as they are called, are made either of brass or iron. The mill, having been turned to proper shape, is laid firmly on some solid substance, and the face that is to be impregnated with diamond-dust is slightly oiled. The dust is then sprinkled thinly over it and tapped lightly with a smooth hammer till the diamond-dust is thoroughly driven into the brass. The brass will bur around it, and hold it securely in place. The oil is used to prevent the dust from bounding off while undergoing the process of hammering.
Files and broaches may be made in the same way. They will cut the hardest material. Polishing broaches are usually made of ivory, and used with diamond-dust loose instead of being driven in. Oil the broach lightly, dip it into the finest diamond-dust, and proceed to use it as you would a brass broach.