The instrument most generally used to prepare the plate is called the rocker (20). Its main element is a curved serrated edge with thread smaller or larger (some 50-100 teeth to the inch), according to the quality of texture required.
The rocker is held with its blade at right angles to the plate, and the curved edge rocked regularly over the whole surface at many angles, causing a uniformly indented surface with a burr to each indentation. A proof taken from this would print black, much of the rich quality of the tone coming from the burr.
Then with the scraper (23, with two cutting edges, a different shape from the ordinary scraper) the engraver removes those portions of the burr where the lights are to appear, working from dark to light. The more of the surface of the grain that is scraped away, the less will the ink be retained by what remains, and if the scraping and burnishing be continued quite to the bottom of the indentations, a smooth surface will be left, which will hold no ink, and print white.
During the last century mezzotint engravers have lessened the arduous labour of preparing the ground by attaching the rocker to a long pole-handle, which can oscillate freely from a moving pivot in any direction. Indications are not wanting, however, to show that some such contrivance of pole and pivot had been known from the very beginning of the art.
