Editing Offset printing (section)

==Plates<!--This section is linked from [[Printer's key]] ([[MOS:HEAD]]).-->==
[[File:Druckplatte offset negativ 01.jpg|thumb|Negative lithographic printing plate]]

===Materials===
The plates used in offset printing are thin, flexible, and usually larger than the paper size to be printed. Two main materials are used:
* Metal plates, usually aluminum, although sometimes they are made of multi-metal, paper, or plastic.<ref name="kipphan209">Kipphan 209</ref>
* Polyester plates, which are much cheaper and can be used in place of aluminum plates for smaller formats or medium quality jobs, as their dimensional stability is lower.<ref name="kipphan209" />

===Computer to plate===
{{main article|Computer to plate}}

Computer-to-plate (CTP) is a newer technology which replaced [[computer-to-film]] (CTF) technology, and that allows the imaging of metal or polyester plates without the use of film. By eliminating the stripping, compositing, and traditional plate making processes, CTP altered the printing industry, which led to reduced prepress times, lower costs of labor, and improved print quality.

Most CTP systems use thermal CTP or violet technologies. Both technologies have the same characteristics in terms of quality and plate durability (for longer runs). However, the violet CTP systems are often cheaper than thermal ones, and thermal CTP systems do not need to be operated under yellow light.

Thermal CTP involves the use of thermal lasers to expose or remove areas of coating while the plate is being imaged. This depends on whether the plate is negative, or positive working. These lasers are generally at a wavelength of 830&nbsp;nm, but vary in their energy usage depending on whether they are used to expose or ablate material. Violet CTP lasers have a much shorter wavelength, 405&nbsp;nm–410&nbsp;nm. Violet CTP is "based on emulsion tuned to visible light exposure".<ref name="bruno126">Bruno, Romano and Riordan 126</ref>

Another process is the computer-to-conventional plate (CTCP) system in which conventional offset plates can be exposed, making it an economical option.