WARNER-POWRIE PROCESS A method of producing screen-plates for colour photography based on the insolubilisation of bichromated fish-glue by the action of light, and subsequent mordanting and staining of the in soluble gelatine. The chief feature of the pro cess is the extreme simplicity of its working, and the absence of overlap of or interspaces between the lines. Briefly, the details of the process are as follows : A sheet of glass is coated with bi chromated fish-glue and exposed under a black and-white line screen in which the black lines are twice the width of the transparent spaces. After exposure the plate is developed in warm water, which removes the gelatine not rendered insoluble by the action of light. The insolu bilised gelatine lines are then mordanted with an acid aniline dye and stained with a basic dye, the result being an insoluble, transparent pre cipitate of dye. The coloured lines thus pro duced are hardened with tannin or other agent, and the whole plate coated with bichromated fish-glue again. After drying, the original black and-white matrix is now arranged in contact with the screen plate so as to cover all the coloured lines thereon and a second exposure made. The result is a second series of lines of
insoluble colloid which may or may not be in contact with the first series. This second series is now mordanted, stained, and hardened pre cisely as at first. Again the plate is coated with bichromated fish-glue, and, after drying, exposed without the intervention of any screen through the back of the plate. The previously coloured lines, which should be the red and green, act as the protection for those portions of the third coating of bichromated colloid immediately over them, whereas in the interspaces, where there is no protecting colour, the bichromated colloid is rendered insoluble, and again mor dented, stained and hardened.
A more recent modification of the process is the placing of the second set of lines at right angles to the first and the subsequent filling up of the third interspace by a similar process as above outlined. This gives a screen with one set of lines and the interspaces divided up into rectangles of the two other colours.