According to the relative position of the printing plate on the graphic and non-graphic area, the common printing methods can be divided into four categories: letterpress printing, gravure printing, offset printing, and stencil printing:
(1) Letterpress printing. The graphic part of the printing plate is raised, which is obviously higher than the blank part. The printing principle is similar to that of the seal. The early woodblock printing, movable type printing, and later lead type printing are all belong to relief printing.
(2) Gravure printing. The graphic part of the printing plate is lower than the blank part. It is often used for the printing of securities such as banknotes and stamps.
(3) Lithographic printing. The graphic part and the blank part of the printing plate are almost in the same plane. The printing method is based on the oil-insoluble principle.
(4) Stencil printing. The graphic part of the printing plate is a hole. The ink is transferred to the surface of the substrate through the hole. Common stencil printing includes a stencil plate and a screen plate.