Mezzotint

Mezzotints are best known for their rich and luscious black tones and soft, subtle areas of light. The resulting image appears hazy and atmospheric, almost like a photograph. Unlike the other intaglio processes, this technique is worked from dark to light; the entire surface of the plate is abraded using a spiked tool called a rocker. These grooves will hold the printing ink and if inked at this point in the process, the plate would print entirely black. To create variations in tone, the artist scrapes and burnishes the abraded plate to smooth out the surface so that those areas will hold less ink and thus yield lighter tones in the image.

Source: http://www.ifpda.org/content/collecting_pr...