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 paper by pressing the two together, using a printing-press, brayer, baren or by techniques such as rubbing with the back of a wooden spoon or the fingers which allow pressure to be controlled selectively. 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 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 Antoon Sallaert created his first monotypes in the early 1640s and is therefore to be regarded as the inventor of this printing process.