A Manual Of Photography

PICTURES ON PORCELAIN TABLETS. 29 of hyposulphite of soda until the pale-yellow tint is removed, and the lights remain quite white. The pictures thus finished have a pleasing and peculiar effect. 6. The appearance of photographic pictures is improved by waxing them, and placing white or coloured paper behind them. 7. Enlarged copies of Daguerreotypes and calotypes can be obtained by throwing magnified images of them, by means of lenses, upon calotype paper. 8. Photographic printing. A few pages of letterpress are printed on one side only of a sheet of paper, which is waxed if thought necessary, and the letters are cut out and sorted; then, in order to compose a new page, a sheet of white paper is reded with straight lines, and the words are formed by cementing the separate letters in their proper order along the lines. A nega- tive photographic copy is then talten, having white letters on a black ground; this is fixed, and any number of positive copies can be obtained. Another method proposed by the patentee is to take a copy by the camera obscura from large letters painted on a white board. 9. Photographic publication. This claim of the patentee con- sists in making, first, good negative drawings on papers prepared with salt and ammonio-nitrate of silver ; secondly, fixing them by the process above described ; thirdly, the formation of positive drawings from the negative copy, and fixing. These claims are taken from the specification as published in the Repertory of Patent Inventions. Section IV.—Pictures on Porcelain Tablets. A third patent has been obtained by Mr. Talbot, mainly in- volving the use of porcelain as a substitute for glass, and con- tains some useful facts noticed by Mr. Malone.. The first part of the patentee’s invention consists in the use of plates of unglazed porcelain, to receive the photographic image. A plate intended for photographic purposes should be made of the finest materials employed by the manufacturers of porcelain ; it should also be flat, very thin, and semi-transparent ; if too thin, so that there would be a chance of breaking, it may be attached by means of cement to a piece of glass, to give it strength. The sub- stance of the plate should be slightly porous, so as to enable it to imbibe and retain a sufficient quantity of the chemical solutions employed. To prepare the plate for use, it is first required to give it a coating of" albumen, or white of eggs, laid on very evenly, and then gently dried at a fire. According as the plate is more