Letterpress printing is the oldest printing method using plates with raised surface. When printing, coat the ink on the surface of matrix, and then press it onto the paper, thus, the ink on the matrix will transfer to the paper. Hand-set, Linotype composition, stereotyping, electrotyping and photo-typography printing are all letterpress printing.
Intaglio printing cuts recessed letters or images by hand or by machine on plates. When printing, first fill the recessed letters or images with ink, then press a piece of paper on it to stick away the ink, forming prints. Printings like etching, engraving and conventional gravure are all intaglio printing.
Planographic printing, also called chemical printing, means the printing images and plates are at the same plane. It displays images on the surface of stone or metal by hand or by machine, then the images are treated by chemicals to reinforce its ink receptivity, while the blank parts show no ink receptivity. The images with ink receptivity transfer to the paper, forming prints. Printings like photo-offset, photolithograph and offset printing are all planographic printing.
Porous printing includes mimeograph, skeleton forme, spraypainting and silkscreen printing. The ink transfers to the stock through the holes on the plates by some pressure and forms images. Mimeograph is the simplest method of porous printing appeared at the end of the 19th century. It is printed on mimeograph paper. The most widely used in porous printing is silkscreen printing.