A plate for the letterpress process is referred to as a relief plate. With a relief plate, the image area is slightly raised above the rest of the plate. It is a direct printing method which means that the image is applied to the substrate directly from the inked plate. Letterpress plates do not require any dampening during the printing process because only the raised image areas of the plates receive ink and the non-image areas remain clean.
The letterpress method is used for some newspaper publishing, labels, and narrow web printing, but it cannot deliver the quality of other printing processes. As a result, it is a fast diminishing printing method.
The original letterpress plate was constructed with movable metal type mounted in a frame called a chase. Each letter or character had to be arranged in the chase which was very time consuming. The type was also backwards or wrong reading so that when the printed impression was made on the paper, it would appear right reading. The need to create more efficient methods of letterpress printing led to the development of better plating techniques.
Stereotype: A stereotype plate is created with the use of a mold of the original metal type. Molten metal is poured into the mold to create the plate. The plates can be flat for use on flatbed presses or they can be produced to conform to the shape of the plate cylinder for a rotary press.
Electrotypes: A mold is also used to create a electrotype plate. The mold is sprayed with a silver coating and it is then electroplated with copper or nickel. The resulting plate is removed from the mold and the back of the plate is filled with lead or plastic for support.
Photoengraving: The plates are prepared by contacting a film negative with the plate and exposing it to a measured unit of light. The plate is then chemically etched, which washes out the unexposed, or non-image areas. The etching removes enough of the plate material in the non-image areas to result in the image areas being raised above the non-image areas. The non-image areas are reduced from the original plate thickness of 0.032" to a thickness of 0.015".