This idea of carving or engraving a design into a metal plate is called intaglio work. Three basic types of intaglio work exist. They are drypoint, engraving, and etching. In drypoint and engraving the design is carved into the metal plate by a sharp pointed tool. These methods both wear away quickly, while the etching method does not because it uses chemical means to deepen the lines.
Etching is the method of using a metal plate to make prints.
The artist then draws or carves his design into the grounded plate, which has been blacked by smoke. This leaves bright drawn lines against the blackened ground. Acid is then applied to the surface of the metal plate. The acid dissolves away the bright metal lines, but does not dissolve through the ground. These lines, that the acid has dissolved, hold the ink for the print.