Typo: A Monthly Newspaper and Literary Review, Volume 4
Under this name has been introduced a system of producing newspaper illustrations, which appears to be the simplest yet in use. A black glass plate or a tin plate coated with black varnish, such as is used by sign painters, is covered with plaster-of-paris (which must be of the best quality and reduced to a fine powder) to about the thickness of a four-sheet card. To the plaster is added some alumn and some sulphate of barium, and a small proportion of glycerine or of gelatine solution to prevent the coating from becoming too brittle. The mixture, in the consistency of a pulp, is applied with a soft camel-hair brush, and allowed to dry. The artist, with a lithographic needle, may then engrave any design or sketch with the greatest ease; the drawing, as the plate is laid bare, appearing in black on a white ground. Errors are easily remedied by filling-in with the preparation. With ordinary roller-composition (to which some solution of bichromate of ammonia has been added) a stereo is now taken from the mould, and when properly mounted it will be found to work in a typographic press, and to be as durable as an electrotype. The bichromate should be dissolved in the proportion of 1 oz. to 1 pint distilled water; to this add J-oz. alcohol. The greater the proportion of bichromate, the harder the plate; but it should have some elasticity. Too great a proportion of the bichromate will make it leathery.