Etching is a printing process. There are several techniques of etching. In engravings, a drawing is engraved in a metal plate with needles. But etchings can also be created with acids. Then a metal plate is coated with wax, in which a drawing is scratched. In an acid bath, the lines of the drawing are etched out.
Aquatint is also an variant of etching. The metal plate is dusted with Rosin powder and between the motes acid can be etched.