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 (relief) in the metal. As a method of printmaking, it is, along with engraving, the most important technique for old-master prints, and remains in wide use today.
Photo-etching is a technique that employs the use of ultra-violet light to fix the image on to the plate. It can be used with both hand-drawn and photographic imagery. In both cases the process involves using a 'positive' on clear film which is contacted against a copper plate covered in a light sensitive emulsion.
When the UV light reaches the coating it is hardened to form an acid resist, and where the light is blocked by the positive image, the coating remains soft and can be developed away, thus exploding the copper for biting in acid. The positive can be created by drawing onto a sheet of film with ink, paint or crayon, or by a photographic technique.