Etching- In 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 or she wants a line to appear in the finished piece, so exposing the bare metal. 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 (it dissolves part of 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.
Intaglio is the 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. It is the direct opposite of a relief print. Normally, copper or zinc plates are used as a surface and the incisions are created by etching, engraving, drypoint, aquatint or mezzotint.
Aquatint is an intaglio printmaking technique, a variant of etching.In intaglio printmaking, the artist makes marks on the plate (in the case of aquatint, a copper or zinc plate) that are capable of holding ink. The inked plate is passed through a printing press together with a sheet of paper, resulting in a transfer of the ink to the paper. This can be repeated a number of times, depending on the particular technique.Like etching, aquatint uses the application of a mordant to etch into the metal plate. Where the engraving technique uses a needle to make lines that print in black (or whatever colour ink is used), aquatint uses powdered rosin to create a tonal effect. The rosin is acid resistant and typically adhered to the plate by controlled heating. The tonal variation is controlled by the level of mordant exposure over large areas, and thus the image is shaped by large sections at a time.
Drypoint is a printmaking technique of the intaglio family, in which an image is incised into a plate with a hard-pointed "needle" of sharp metal or diamond point. The plate is copper, or zinc, or plexiglas are also commonly used. Like etching, drypoint is easier for an artist trained in drawing to master than engraving, as the technique of using the needle is closer to using a pencil than the engraver's burin.The lines produced by printing a drypoint are formed by the burr thrown up at the edge of the incised lines, in addition to the depressions formed in the surface of the plate. A larger burr, formed by a steep angle of the tool, will hold a lot of ink, producing a characteristically soft, dense line that differentiates drypoint from other intaglio methods such as etching or engraving which produce a smooth, hard-edged line. The size or characteristics of the burr usually depend not on how much pressure is applied, but on the angle of the needle.