Kate Cheney Chappell - Printmaking

Monotypes are by definition, one-of-a kind prints. They can be experimental and painterly. Plates may be plexiglas or metal, but the image produced is wiped clean after one or two passes through the press. The additive approach paints or applies areas of ink to the plate to create the image; subtractive approach inks the entire plate and wipes areas away or masks areas with stencils to create the image.

People use the terms interchangeably, so it can be confusing!
Monoprints are unique, individual images, but usually have a "repeating matrix" (a part that repeats) or elements of other printmaking techniques. Often, a suite of prints will be made, which are numbered by Roman numerals, e.g., I/VIII, II/VIII, etc. Monotypes are signed using "1/1"(Arabic number).
Monotypes have experienced a recent surge in popularity among painters; nevertheless, there is a tradition of monotype in art. Degas made good use of this medium. (see his monotype, Three Ballet Dancers, 1878; also Degas Monotypes, by Eugenia Parry Janis, 1968).

A collagraph is a print made from a plate to which material has been adhered, a "collage for printmaking", if you will. The plate may be as simple as cardboard or mat board. Various materials are glued on. Gesso may be used as a ground into which marks are made that set the image as it dries. Then the whole plate is sealed with acrylic medium or shellac. When dry, it can be inked, wiped with a tarlatan cloth (like an etching), and printed. The plate can be used again and again, allowing for experiments in color and wiping.