A rocker (berceau in French) is a tool for producing a regular pattern of tiny holes (and burrs) on a mezzotint copper plate. It is used to prepare the master plate by creating countless holes on the plate surface.

It consists of a sharp, arched blade on one end and a wooden handle on the other. The back of the blade is channeled with regularly-spaced parallel grooves. It is tilted slightly in the direction of movement and rocked from side to side on the plate to move it gradually along. The grooves on the rocker thus produce holes with tiny burrs on the plate surface. This is repeated vertically, horizontally and diagonally (in both directions) until a countless number of holes is created. This is known as “roughening”. It is called a rocker because it is rocked from side to side like a cradle.

Various types of rockers with different size blades and number of grooves are available. A suitable type should be selected according to the shape of the area to be roughened and how densely black (hole) it is going to be, but this does not affect the time and effort required for the roughening process. To roughen the plate with less effort, mezzotint rocker machines may be used. There are hand-operated and electrically operated 　models but they both use rocker blades that have been detached from the handle. This machine improves efficiency by allowing the user to make plates more quickly.

A halftone comb is another instrument that can be used for making mezzotint plates. It is used by placing the blade on the plate and pulling it straight along a ruler. This enables delicate parallel lines to be drawn on the plate surface. As with a rocker, this process is repeated vertically, horizontally and diagonally (in two directions). A parallel line effect, similar to that of a halftone comb, can also be obtained by bundling several cutters together and using this to prepare the plate.

Rockers can be purchased at art supply stores that handle printing supplies.