GRAVURE PRINTING

The Bohemian Karel Klíč made photogravure a practical commercial process in 1878. An image is etched in the copper surface of the printing cylinder as pits or wells of different depths. In rotogravure printing, the cylinder rotates through a trough filled with fast-drying ink. A thin steel doctor blade removes the ink from the surface but not from the wells. The cylinder comes in contact with the paper, which draws the ink out of the wells. Because of the various depths of the wells, a full range of tonal values can be printed; in reproducing illustrations, gravure comes closest to simulating continuous-tone copy. In {{link=colour printing">colour printing , a separate cylinder is prepared for each colour. See also letterpress printing ; offset printing .