Improvements in or relating to the Production of Printing Plates and Surfaces

14,513. Schmidt, J., and Gruber, R. June 25. Lithographic and like printing.-A zinc or other metal plate is cleaned with dilute sulphuric acid and emery, pumice-stone, or the like and then with a mixture of water, hydrochloric acid, and alum. The dried plate is coated with a sensitized layer, consisting of gelatine and ammonium bichromate, and is exposed under the picture to be copied in an ordinary printing-frame. The plate is developed in water, dried, and powdered with Syrian asphalt which is then melted. The asphalt adheres to the unexposed parts of the plate and the rest of the sensitized layer is removed by means of a mixture of hydrochloric acid and gum water. The plate is then washed with turpentine and sulphuric ether and is rolled up with ink which adheres only to the asphalt.