| What
Is Offset Lithography?
 n
offset lithography (also known as plantographic) printing, plates
carry both the image and non-image areas on the same level (unlike
letterpress where areas are raised to
catch ink). The transfer of ink is controlled by an unlikely principle.
The principle that oil and water don't mix.
Image areas are photographically transferred to
thin metal plates which are treated chemically to accept oil-based
ink but repel water on the image areas. Conversely, non-image areas
accept water but repel the oil-based ink.
A plate first contacts rollers of a clean solution
or water and then is inked by other rollers. The oil-based ink "sticks"
to the image area. The inked image is then transferred from the
plate to a rubber blanket. The rubber blanket then transfers the
image onto the paper's surface.
Because of the resilience of the rubber blanket,
it's possible to use offset lithography printing on a wide variety
of surfaces and for large quantities. Both spot
colors and CMYK colors can be used
with this process.
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