offset printing

Most common commercial printing technology in which the image to be printed is photographically transferred to a metal or plastic printing plate which is wetted by water. The image portion of the plate repels water but picks up oil-based ink from a roller, and the non-image areas retain water but repel the ink. The inked image is then transferred first to a sheet of rubber or plastic (called a 'blanket') which transfers it to the paper. The objective of this double transfer it to avoid the printing plate's contact with paper (and thus reduce its wear) which has a rougher surface than the blanket.