Note: Do not rely on this information. It is very old.
Mezzotint
Mezzotint, a method of engraving on steel or copper. First the whole surface of the plate is roughened, and then the roughness is lessened or removed for the lighter parts of the engraving. This process was invented (1643) by Van Siegen, a Dutchman. Its great drawback is that it does not allow of sharp and clear delineation of form.