10,649. Wilkinson, W. J. May 31, 1912, [Convention date]. Etching. - In the production of half-tone relief printing-plates for ordinary or colour printing the plate is given two etchings, the first being an ordinary flat etching and the second an etching through a film or coating obtained photographically and adapted to retard the etching differentially in accordance with the different shades of the picture to be reproduced. Two negatives are taken from the same position, one through a screen, and the other without a screen, but through a clear glass plate of the same thickness as the screen. The first negative is used to obtain the first etching resist. The flat etched plate is resensitized, and the second negative is printed in register to produce the differentially permeable coating for the second etching.
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