So far, indeed, from the art being lost, there is no doubt that a better material and better colors are now made; and those who examine the works produced by Hardman, Ballantine, Chance, and other manufacturers of our country, and those of Munich and other continental works, will not easily believe that the ancients were more successful in their designs than the moderns. But besides the pot-metal and flashed glasses before mentioned, there are two other methods of coloring and producing pictorial effects on glass. The first is by staining, that is to say, painting the glass with various materials, usually metallic oxides finely powdered, and mixed with oil of spike or some other volatile medium; the glass is then placed in a furnace, in which it is made red hot, and a deep stain of the color required is produced on the glass. This process enables the artist to produce a complete picture on one piece of glass; whereas, by the older method, the picture had to be made up of a vast number of pieces set in a slender lead-framing. Generally, both methods are employed in pictorial windows, as the staining enables the artist to give the human features. But staining does not produce the same brilliancy of color, and lessens tile transparency of the glass, hence it is in less esteem.
Another mode of decorating glass is by using the opaque, or nearly opaque, enamel colors, and after the design is produced with these, to fix them by firing: this is a beau tiful art, and is variously employed.
Lately another and very remarkable invention for decorating glass has been patented by M. Joubert of Bayswater, London—viz., the fixing of photographic pictures upon this material. The sensitive salt used to receive the picture is one which will stain glass; therefore, on firing, the picture is deeply burned into the glass, and cannot be effaced; most beautiful effects are thus produced; natural landscapes and pictures may be transferred with most perfect fidelity.
and can be easily ground with sand and water, so that the ornamental effect of vessels and other objects of flint-glass may be very greatly enhanced. Sand, however, leaves a rough surface, and destroys the transpar ency; hut this is easily restored by other materials, as emery, putty-powder (oxide of tin), tripoli, red oxide of iron, or colcothar, etc. The cutting and polishing are effected with wheels or disks of sandstone, wood, and metal. Very fine engraving is done with pointed metal tools and diamond-dust: and the latest improvement, intro duced by Messrs. Pillalt and Word of London, is using minute wheels. which revolve rapidly, and are dressed with emery or diamond-dust.
Time polishing of lenses for optical instruments and for light-houses is an art of very great importance, requiring skill. Much of, the polishing of the larger lenses is effected by the aid of machinery, and perhaps no combinations of mechanical art are more wonderful than the machines by which the Messrs. Chance of Birmingham polish the prisms and lenses for eatoptrie and dioptric light-houses.
Glass in a liquid form has lately been extensively made under the name of soluble glass or silicate of soda; it is silica, or sand, dissolved in a solution of caustic soda. This liquid when used as a varnish, is said to protect stone and other materials from the injurious action of the weather, arid for this purpose is now employed to arrest the decay of the stone of the new houses of parliament. It has been recommended to be used as a dressing for muslins and other fabrics, to render them fire-proof. Several methods have been devised for tempering, hardening, or toughening glass; but none has yet attained commercial importance.