Monotyping is a type of printmaking made by drawing or painting on a smooth, non-absorbent surface. The surface, or matrix, was historically a copper etching plate, but in contemporary work it can vary from zinc or glass to acrylic glass. The image is then transferred onto a sheet of paper by pressing the two together, usually using a printing-press. Monotypes can also be created by inking an entire surface and then, using brushes or rags, removing ink to create a subtractive image, e.g. creating lights from a field of opaque colour. The inks used may be oil based or water based. With oil based inks, the paper may be dry, in which case the image has more contrast, or the paper may be damp, in which case the image has a 10 percent greater range of tones.
Monotyping produces a unique print, or monotype; most of the ink is removed during the initial pressing. Although subsequent reprintings are sometimes possible, they differ greatly from the first print and are generally considered inferior. These prints from the original plate are called "ghost prints." A print made by pressing a new print onto another surface, effectively making the print into a plate, is called a "cognate". Stencils, watercolor, solvents, brushes, and other tools are often used to embellish a monotype print. Monotypes can be spontaneously executed and with no previous sketch.
There is still no certainty as to who was the inventor of the monotype process. The Italian artist Giovanni Benedetto Castiglione (1609–64) is often credited as being the first artist to produce monotypes. He made brushed sketches intended as finished and final works of art. He began to make monotypes in the mid 1640s, normally working from black to white, and produced over twenty surviving ones, over half of which are set at night. It is believed that the Flemish artist Antoine Sallaert created his first monotypes in the early 1640s and is therefore to be regarded as the inventor of this printing process. Both artists used the new technique in different ways. Castiglione created most of his monotypes as black-field images by wiping away ink on a prepared plate thus producing white and grey lines. Sallaert, on the other hand, brushed bold, tapering lines onto the printing surface with meticulous precision. It is likely that Sallaert's monotype style was influenced by the chiaroscuro woodcuts of the Dutch engraver Hendrik Goltzius. Sallaert found in the monotype a technique which was the closest to drawing and oil sketching. His monotypes and drawings are characterised by swelling lines and tapering ends. He often added by hand white highlights to his monotypes. Sallaert clearly appreciated in the monotype technique the freedom to design on a plate before printing it on paper.