Offset printing is a process where
the printing is first done on the rubber surface of a rotating cylinder.
The impression is transferred to paper by the pressure of other cylinders.
The term offset describes the printing, or offsetting, of the ink from
the rubber.
Offset lithography is generally accomplished
on a press with three cylinders. A lithographic plate of aluminum or zinc
is wrapped around the first cylinder. The plate prints on a second cylinder
that is covered by a rubber blanket. The impression on the rubber is then
printed on the paper which is on the third cylinder. This third cylinder
has steel fingers called grippers that hold the paper in position while
it is squeezed against the rubber surface.
The use of offset printing for movie
posters was first undertaken by Morgan Litho in the 1930's. This process
was more economical, and the offset plates were easier to handle and store.
However, although some early examples were able to duplicate the full
color of stone lithography, posters began
to lose their color depth and subtleties as the offset printing process
evolved.
Most of the materials printed today
by studios are accomplished using this offset printing process, which
has been further advanced through the use of computer technology. Today's
posters are more defined and detailed, but many collectors do not feel
that they can match the lushness of color and tone that the early stone
litho posters were known for.
