Sand Blast, a method of engraving figures on glass or metal, or cutting away or boring holes in hard substances, by a rapid stream of sharp sand, invented by Mr. B. C. Tilghman of Philadelphia. The jet of sand may be driven by a blast of steam from a boiler, at high pressure (from 50 to 300 lbs. per square inch), or by an air blast produced by a fan blower revolving with great velocity (a 30-inch fan 1,500 to 2,000 times per minute). The sand is contained in a hopper, and is let down through a tube with a fine orifice, which may be inclined at any desired angle. Surrounding the sand tube is the blast pipe, the effect being to carry the stream of sand with nearly the velocity of the steam or air jet against the object to be operated on, which is placed in a box, and adjusted by means of slides so that it may be moved in front of the jet as the figures are being cut. The box must have openings for the exit of the air. In an experiment with this apparatus a hole an inch and a half in diameter and of the same depth was bored through a piece of corundum in a little less than half an hour, the sand being driven by a steam jet at 300 lbs. pressure per square inch. A diamond was easily reduced in weight and a topaz completely dissipated in one minute.
Patterns of objects may be laid upon the glass in the manner of stencil plates, and engraved with great facility. An engraving of a photographed coating of gelatine upon glass may also be taken.