A monoprint is a single impression of an image made from a reprintable block. Materials such as metal plates, litho stones or wood blocks are used for etching upon. Rather than printing multiple copies of a single image, only one impression may be produced, either by painting or making a collage on the block. Etching plates may also be inked in a way that is expressive and unique in the strict sense, in that the image cannot be reproduced exactly. Monoprints may also involve elements that change, where the artist reworks the image in between impressions or after printing so that no two prints are absolutely identical. Monoprints may include collage, hand-painted additions, and a form of tracing by which thick ink is laid down on a table, paper is placed on top and is then drawn on, transferring the ink onto the paper.