Glass Glass Working
Glass, Burnt in Photographs on. All the methods indicated under the heading Enamel and Ceramic Photographs are available with glass as a basis. The glass is laid on an even bed of powdered plaster of Paris, when fired in the muffle. The following list of books on photography in vitrifiable colours may be of service: - "Die Photokeramik," by T. Krtiger: Vienna, Pest, and Leipzig, 1879, Hartleben's Verlag; "Photographische Schmelzfarbenbilder " : Diisseldorf, 1882, Ed. Liesegang's Verlag ; 11 Traite Pratique Des Emaux Photographiques," by Geymet: Paris, 1885, Gauthier-Villars; " Procedes Photographique sur la Porcelaine," by E. Godard: Paris, 1888, Gauthier-Villars; 11 Heliographie Vitrifiable," by Geymet: Paris, 1889, Gauthier-Villars ; " Photoceramics," by E. Henry and H. S. Ward : London, 1895 ; " Photographische Schmelzfarbenbilder : auf Email, Porzellan und Glass," neu barbeitet von R. E. Liesegang: Diisseldorf, 1898, Liesegang's Verlag.
Glass Silvering. The reversing mirror, or the hypotenuse of the reversing prism, is now always silvered rjy some modification of Liebig's process, (For instructions, see Mirror, Silvering.)
Glass, Soluble. Basic alkaline silicates dissolve in water, and are sold as soluble glass. Used in preparing substrata for Collotype (q.v.) and in other cases where it is desirable that a gelatine film should adhere very firmly to a glass plate.
Glass Working. The following notes will be serviceable : -
Cutting with diamond. The main point is keeping the dia-mond at the same angle, when once the cutting angle is found - this involving a wrist action which requires some practice. When the true cut is being produced, a peculiar hissing sound can be distinguished, and the best diamonds produce no per-ceptible scratching or abrasion of the glass when the best cutting angle is realised; so that the true cut can hardly be seen when looked at perpendicularly.
Filing. An ordinary file, kept moist with a saturated solution of camphor in oil of turpentine can be used with excellent effect.
Grinding. See Focussing Screen.
Leading a crack. A crack will usually follow a heated iron rod as large as a pipe stem, the end of the rod being kept a quarter of an inch in advance of the crack. This process is often useful in making jars or funnels of broken bottles,