Platemaking
After the copy has been shot and the film developed, you get a film negative. It is from this film negative that the printing plate is made. (Although printing plates can also be made from film positives we shall base our discussions only on those made with film negatives.)
All printing plates have one thing in common: the area to be printed must stand apart from the non-printing area. There are three basic ways to separate the printing area from the non-printing area: (1) raise the printing area, (2) lower the printing area, or (3) leave both areas on the same level and treat the plate chemically so that the printing area accepts ink while the non-printing area rejects it. These three ways form the bases of our three major printing processes: letterpress, gravure, and offset lithography.
Although there is a great deal of difference between letterpress, gravure, and offset plates, they are made in much the same way. In all cases the plates are made photographically by using a film negative, a light-sensitive metal plate, and chemicals.