Paper and Printing Recipes / A Handy Volume of Practical Recipes, Concerning the Every-Day Business of Stationers, Printers, Binders, and the Kindred Trades

by John Sawtelle Ford

An Improved Process of Photo-Engraving.

The metal plate, of copper or zinc, is coated with a very thin layer of bitumen of Judæa, and when this coat has become perfectly dry, a film of bichromatized albumen is flowed over the plate. It is next exposed in the camera, and afterwards washed with water, in order to dissolve all the albumen which has not been rendered insoluble by the luminous action; it is then treated with spirit of turpentine, which dissolves all those parts of the layer of bitumen that have become exposed. The plate can now be attacked directly by water acidulated with from four to six per cent of nitric acid. The great advantage of this method consists in the high sensitiveness of the bichromatized albumen, at the same time preserving the solid reserve produced by the bitumen of Judæa on a metallic surface.