Monotype

In this technique the artist creates a composition in printing ink or paint on any smooth surface which is then covered with a sheet of paper and passed through a press, transferring the image to printing paper. Because of the smooth surface, the pressure applied irrevocably alters the composition, making multiple impressions nearly impossible. In the rare instance that two prints can to be pulled from the same surface, one will be strong and the other weak. 

Source: http://www.ifpda.org/content/collecting_pr...