(2) Small, rough, refuse diamonds, set in the end of a tin tube, make effective drills for glass.

(3) Richter and Co., Chemnitz, have a way of impregnating thin German silver discs (15 to 25 mm. diameter) with diamond, so that when fitted to a quickly - rotating tool, these cut through glass or porcelain in a few seconds, or effect any desired carving with great accuracy. With cylinders made on the same principle, round holes can be quickly and exactly made. The wear of the implement, even after much use, is hardly perceptible.

(4) A simple method of perforating glass with the electric spark is described by Fages. The apparatus required consists (a) of a rectangular plate of ebonite, its size, for a coil giving 12 centimetre sparks, about 18 centimetres by 12 j (b)) of a brass wire passing under the plate and having its pointed end bent up and penetrating through the plate (not farther). This wire is connected with one of the poles of the coil. A few drops of olive - oil are placed on the ebonite plate about the point, and the piece of glass to be perforated is superposed, care being taken not to imprison any bubbles of air. The olive - oil perfectly accomplishes the object of insulating the wire. One has then only to bring down a wire from the outer pole of the coil, on the piece of glass, above the point of the lower wire, and pass the spark. By displacing the glass laterally, for successive sparks, it is easy to make a close series of holes in a few seconds.

Engraving Glass

Plante has suggested a process for engraving on glass by electricity:- The plate is covered with a concentrated solution of potash nitrate, put in connection with one of the poles of the battery, and the design is traced out by a fine platinum point connected to the other pole. The results are said to be of wonderful delicacy. Bound articles can be treated by adding gum to the solution to make it adhere.

Frosting Glass

Make a saturated solution of alum in water, and wet the glass with the liquid. It is advisable to have the glass in a horizontal position, as the solution is not likely to drain off. The more slowly it is cooled, the more perfect will the crystals be; you can with that intention warm the glass. You may, if you choose, colour the alum solution with cochineal, and of course the more solution you use the thicker you will have the crystals.

Roughening Glass

This may be produced by the recently - invented sandblast process, based upon the principle that if a stream of sand be made to fall through a vertical tube open to the air at the top, and the falling sand and air be received in a suitable closed vessel below, a jet or current of compressed air can be obtained. The entire surface of a vessel may thus be roughened, or, if parts are protected by a suitable medium, only the exposed portions will be abraded. By this means, very delicate patterns may be produced. Glass may be etched by the action of hydrofluoric acid, either in solution or in the form of gas. The variety in depth of incision, which gives the chief beauty to engraved glass, cannot be gained by either of these processes.

Stoppering Glass

In stoppering a bottle, there are 2 processes: (1) The mouth of the bottle is opened to the required size by a steel cone revolving in a lathe; (2) the stopper is fixed in a wooden chuck, reduced to proper dimensions, and finally ground into the mouth of the bottle.