The external surface of the board is shaped with a gentle curve either across its whole surface (full cushion) or around the borders of the board (peripheral cushion).
The border of the board is reduced in thickness around its edges by means of a gentle curve, which leaves the central part of the board flat. This was less expensive to execute than a full cushion, but also allowed the use of panel stamps to decorate the flat area in the centre.
The whole surface of the board is shaped in a gentle curve from spine to fore-edge and head to tail, to create a continuous convex shape, usually taking the edges of the board down to about 50% of their original thickness. Such a shape will be found on the external surface of a board only.
Presses used in intaglio printing in which the plate, paper, and cushioning blankets pass between cylinders that exert pressure, forcing the paper into the grooves in the plate which hold the ink.
The Arts and Architecture Thesaurus Online, The Getty Research Institute.