Etching is the most widely used form of the ‘intaglio’ processes where the line and tone of an image are created by exposing areas of a metal plate to acid.
The process of making a print: The surface of a metal plate is covered in wax and the artist then creates their image by scratching into the wax. The plate is then immersed in an acid bath. The areas of the plate not covered by the wax are then ‘eaten’ away by the acid creating a grove for the ink to sit in. The plate is then covered with ink most of which is then rubbed off so only in ink in the groves remains. The plate is then placed face up on the press bed and covered with dampened paper which in turn is covered with layers of finely woven wool "blankets". All this is run through the press which looks a bit like a mangle which forces the damp paper into the etched areas of the plate picking up the ink.
Photogravure (or heliogravue) is an intaglio printmaking or photo-mechanical process whereby a copper plate is coated with a light-sensitive gelatin tissue which had been exposed to a film positive, and then etched, resulting in a high quality intaglio print that can reproduce the detail and continuous tones of a photograph.
Photo-etching requires the image to be broken down into halftone dots on film of the same size that you want the image before chemical milling the sheet to corrosively machine away selected areas and create the image.
History: Etching was used for decorating metal from the fourteenth century, but was probably not used for printmaking much before the early sixteenth century. Since then many different etching techniques have been developed, which are often used in conjunction with each other.
‘intaglio’ family of printing and printmaking techniques in which the image is incised into a surface, and the incised line or sunken area holds the ink.