An indirect Intaglio technique in which a piece of metal sheet (the plate) – usually copper or zinc – is covered with an acid resistant coating into which is drawn the image revealing the metal. When immersed in acid only these parts of the metal are eaten away. The longer the time in the acid, the deeper will be the line and the darker it will appear when printed because it holds more ink.
This is the term used to describe the process of adding tone (not colour) to a line etching. Instead of a surface of wax the metal plate is given a thin layer of resin dust which, when heated, adheres to the metal. The resin protects the metal from acid but allows the acid to attack the metal between the resin grains. This produces a fine network of “valleys” which hold ink. Varying the depth of the valleys will vary the amount of ink held and thus vary the tone value.
Printing the Plate
The plate is heated and stiff ink rubbed into it, then using small circular motions and a pad of wiping canvas, excess ink is removed, this is repeated, gradually using cleaner canvas. Finally, the plate is ‘hand-wiped’; this removes plate tone and allows the lines to become more sharply defined. The paper for printing needs to be soaked and laid down for a number of days, this softens the paper, so that when it is printed it is forced more easily into the grooves of the plate. The pressure required for printing is great, several tons, and this is achieved by using an Etching Press. The press is a large mechanical device, with two main rollers placed above each other with a flat bed of steel that travels between the two. The sliding bed is moved from one end of the press to the other, with the inked plate resting face up. The paper is placed over it and then several wool blankets on top. The blankets are compressed as the rollers move, thus forcing the paper into the plate and so lifts out the ink. Once the plate is printed, the paper is carefully removed from the plate, a sheet of tissue paper is laid over the print and it is left between sheets of blotting paper under a heavy board to dry for a few days. The plate needs to be re-inked and re-wiped for each print!