Epple developed an early interest and passion for graphic arts such as woodcuts,lithographs and engravings. He devoted much of his artistic energy to the art of engraving on copper or other metal plates which has a long and distinguished history in German art going back to Albrecht Durer, Martin Schongauer and Lucas Cranach.
In this process, known as intaglio printing, the artist cuts the lines to be printed into a metal plate by means of a cutting tool called a burin, held in the hand. To print an intaglio plate, ink is applied to the surface by wiping and/or dabbing the plate to push the ink into the recessed lines, or grooves. The plate is then rubbed with cloth to remove most of the excess ink. The final smooth wipe is often done with newspaper leaving ink only in the incisions. A damp piece of paper is placed on top of the plate, so that when going through the press the damp paper will be able to be squeezed into the plate’s ink-filled grooves.The paper and plate are then covered by a thick blanket to ensure even pressure when going through the rolling press. The rolling press applies very high pressure through the blanket to push the paper into the grooves on the plate.https://en.wikipedia.org/wiki/Intaglio_(printmaking)