By one method the surface of the object is first coated with tinfoil on which the artist traces his design, and this is then coated with melted transparent wax. Then when the wax is hardened it is cut away along the lines already indicated, and seen through the wax. The object now is subjected to the blast, and as the sand will not penetrate a softened material sufficient to abrade a surface beneath, the exposed portions alone will be cut away. The sand after it strikes is carried off by a blast to some receptacle, from which it is returned to its former place for further use. Other means may be used in the place of a slitted box, as a small or larger blow-pipe; but the driving of the sand, or similar abrading material, with great force by the steam or air blast, is the essential feature of the process. _Emery_, that variety of the mineral corundum, consisting of crystalline alumina, resembling in appearance dark, fine-grained iron ore, ranking next to the diamond in hardness, and a sister of the sapphire and the ruby, has long been used as an abradant. The Eastern nations have used corundum for this purpose for ages. Turkey and Greece once had a monopoly of it. Knight says: “The corundum stone used by the Hindoos and Chinese is composed of corundum powdered, two parts; lac resin, one part. The two are intimately mixed in an earthen vessel, kneaded and flattened, shaped and polished. A hole in the stone for the axis is made by a heated copper rod.” However ancient the use of artificial stones for grinding and polishing, nevertheless it is true that the solid emery wheel in the form that has made it generally useful, in machines known as _emery grinders_, is a modern invention, and of American origin. In the manufacture of such machines great attention and the highest scientific skill has been paid, first, to the material composing the wheel, and to the cementing substances by which the emery is compacted and bound in the strongest manner, to prevent bursting when driven at great speed; secondly, to the construction of machines and wheels of a composition varying from the finest to the coarsest; and thirdly, to the proper balancing of the wheels in the machines, an operation of great nicety, in order that the wheel may be used on delicate tools, when driven at high speed, without producing uneven work, marking the objects, or endangering the breaking, or bursting of the wheel.