Intaglio printmaking makes marks on the matrix (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 acid to make the marks in 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 acid exposure over large areas, and thus the image is shaped by large sections at a time. Another tonal technique, mezzotint, begins with a plate surface that is evenly indented so that it will carry a fairly dark tone of ink. The mezzotint plate is then smoothed and polished to make areas carry less ink and thus print a lighter shade; or, beginning with a smooth plate, areas are roughened to make them darker; or, these two techniques may be combined.
Francisco Goya: Spanish (1746-1828)
Estan calientes, (They are Hot)
Aquatint is a method that allows the artist to print tonal passages in an etching. The artist applies a very fine dusting of powdered rosin to the etching plate. When this rosin dust is heated it bonds to the metal plate with each dust particle forming a minute area that resists acid. The plate is bitten in an acid bath, resulting is a fine texture that will hold ink. The longer the plate is left in the acid the deeper the texture will be bitten and the darker it will print. Goya was a masterful aquatint artist. He has bitten this plate several times, using an acid-resistant "stop-out" to protect the areas he wanted to remain lighter. If you look at the monk's knee you can see what appear to be white brush strokes. This is where Goya applied stop-out with a brush before the first acid bath, leaving the metal plate entirely unbitten. These areas of the plate hold no ink and therefore allow the white of the paper to show through. Subequent immersions in the acid result in increasing dark passages (compare the top left and right). Below the monk's knee you can see where Goya has gone back to work on an aquatint passage with a burnisher. The burnisher smooths the aquatint texture and creates lighter areas like the wispy areas below the knee. (Spencer Museum of Art)
Although aquatint was employed most elaborately by English etchers, it became the medium of masterpieces in the hands of the great Spanish painter Francisco Goya. After starting his etchings with brittle but assertive lines, Goya proceeded to cloak them in haunting aquatint shadows. A graphic artist of astounding ingenuity and sensitivity, Goya created four great cycles of etchings to which aquatint contributed emotional depth: Los Caprichos (1799) (18.64.43); Los Desastres de la Guerra (1810–19); La Tauromaquia (1816); and Disparates (ca. 1816–23).