A form of engraving where the metal printing plate is indented by rocking a toothed metal tool across the surface. Each pit holds ink, and if printed at this stage the image would be solid black. The printmaker works from dark to light by gradually rubbing down or burnishing the rough surface to various degrees of smoothness to reduce the ink-holding capacity of areas of the plate. The technique was developed in the seventeenth century, and became particularly popular in eighteenth-century England for reproducing portrait paintings. It is renowned for the soft gradations of tone and richness and velvet quality of its blacks.