Monoprinting is a form of printmaking that uses a matrix such as a woodblock, litho stone, or copper plate, but produces impressions that are unique. Multiple unique impressions printed from a single matrix are sometimes known as a variable edition. There are many techniques used in monoprinting, including collagraph, collage, hand-painted additions, and a form of tracing by which thick ink is laid down on a table, paper is placed on the ink, and the back of the paper is drawn on, transferring the ink to the paper. Monoprints can also be made by altering the type, color, and viscosity of the ink used to create different prints. Traditional printmaking techniques, such as lithography, woodcut, and intaglio, can be used to make monoprints.