Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio in the metal. In modern manufacturing, other chemicals may be used on other types of material. As a method of printmaking, it is, along with engraving, the most important technique for old master prints, and remains in wide use today. In a number of modern variants such as microfabrication etching and photochemical milling it is a crucial technique in much modern technology, including circuit boards.
In traditional pure etching, a metal plate is covered with a waxy ground which is resistant to acid. The artist then scratches off the ground with a pointed etching needle where he or she wants a line to appear in the finished piece, exposing the bare metal. The échoppe, a tool with a slanted oval section, is also used for "swelling" lines. The plate is then dipped in a bath of acid, known as the mordant or etchant, or has acid washed over it. The acid "bites" into the metal to a depth depending on time and acid strength, leaving behind the drawing carved into the wax on the plate. The remaining ground is then cleaned off the plate.