Etching is 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 (the original process—in modern manufacturing other chemicals may be used on other types of material). As an intaglio method of printmaking it is, along with engraving, the most important technique for old master prints, and remains widely used today.
techniques
basic method
In pure etching, a metal (usually copper, zinc or steel) 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/she wants a line to appear in the finished piece, so 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, technically called the mordant (French for "biting"), or has acid washed over it. The acid "bites" into the metal, where it is exposed, leaving behind lines sunk into the plate. The remaining ground is then cleaned off the plate. The plate is inked all over, and then the ink wiped off the surface, leaving only the ink in the etched lines.
The plate is then put through a high-pressure printing press together with a sheet of paper (often moistened to soften it). The paper picks up the ink from the etched lines, making a print. The process can be repeated many times; typically several hundred impressions (copies) could be printed before the plate shows much sign of wear. The work on the plate can also be added to by repeating the whole process; this creates an etching which exists in more than one state.
Etching has often been combined with other intaglio techniques such as engraving or aquatint.
aquatint
Aquatint is a variation in which particulate resin is evenly distributed on the plate, then heated to form a screen ground of uniform but less than perfect density. After etching, any exposed surface will result in a roughened (i.e. darkened) surface. Areas that are to be light in the final print are protected by varnishing between acid baths. Successive turns of varnishing and placing the plate in acid create areas of tone difficult or impossible to achieve by drawing through a wax ground.
hard grounds
There are many ways for the printmaker to control the acid's effects. Most typically, the surface of the plate is covered in a hard, waxy 'ground' that resists acid. The printmaker then scratches through the ground with a sharp point, exposing lines of metal that are attacked by the acid.
carbograph
This is an etching technique invented in 2006 by the U.S. printmaker Rand Huebsch. Tiny particles of carborundum grit are mixed into the acid-resistant ground, which is brushed onto the bare metal as usual and allowed to dry. When that mixture has dried, the metal stylus is used on the plate and thereby removes some of the grit particles, so that minuscule areas of copper are exposed to the acid and etched; they will eventually hold the ink for the printing process. Thus the image on paper has a texture similar to that of a charcoal drawing.
dry point etching
With a steel or diamond needle, the plate is carved directly. There is no usage of acid (thus called a dry procedure). The ink is kept between the carvings and the burr. Because off the weakness of the burr, each cleaning of the plate, the image fades. The edition of these etchings is therefor rather small.
edition
The edition of an etching is influenced by the technique and the personal preferences of the artist. Each time the plate is cleaned, the image fades a little bit. Some techniques allow editions of 75 à 100, others only allow up to 30 pieces. Each piece that is approved by the artist gets a unique number and is signed. After printing, the plate is often destroyed or damaged to prevent that the work would be reproduced.