In etching, the artist draws with a needle on to a copper, zinc or steel plate that has been covered with an acid resistant wax. When the plate is immersed in acid, the bare metal, exposed by the lines of the drawing, is eroded. The depth of the 'etch’ is controlled by the amount of time the acid is allowed to ‘bite’ the metal. The longer in acid, the deeper the line and the darker it will print. In order to obtain a print, viscous greasy ink is pushed into the etched grooves, then the surface is wiped clean with muslin, leaving only the etched areas retaining ink. The actual impression is made with a copper plate press, which is similar to an old washing mangle, with a large plank or 'bed’ between the rollers. The plate is placed on the bed, covered with dampened paper and backed with three or four felt blankets. These are then passed through the press under high pressure; the malleable paper is forced into the cuts and ridges in the plate and thus picks up the ink. When the paper is finally peeled off, it reveals a faithful mirror image of the etched drawing. This inking procedure is then repeated for each print in the edition. In aquatint etching resin powder is melted onto the metal plate to produce a tonal, textured surface and more than one colour may be used. Because etching plates are inked by hand, each print is unique.