Press Processes, Continued
Lithography is based on the principle that oil and water do not mix.
Lithography originated with a hand drawing in greasy crayon on a flat
surface of limestone. The greasy image repelled water and retained oily ink
to transfer an image to paper. The nongreasy areas, flushed clean with water
did not retain ink and resulted in a nonimage or open area. Offset
lithography is the most widely used form of printing in Navy print shops. A
photographically sensitive metal plate of aluminum or zinc retains the image
on its surface after exposure to light and chemical development. The image
area retains ink and transfers the image to a rubber blanket (blanket cylinder)
which in turn transfers the image to an impression cylinder. The impression
cylinder transfers the image to the paper surface.
Figure 1-3 shows the basic offset lithographic process.
Figure 1-3.Offset lithographic printing.
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