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Lithography,
unlike other printing techniques, depends not on differences in
surface elevation, but on the simple principle that grease and water
do not mix. Invented by Aloys Senefelder in 1796, lithography is
a flat surface or planographic printing method. The commercial and
artistic possibilities of the technique were quickly recognised.
Artists could draw directly onto the lithographic stone, producing
images of great expressiveness and freedom of line, and the process
was cheaper than etching.
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The
design requirements for an effective posterthat it catches
the eye and imparts its message quickly, that it utilises simple
forms with large areas of uniform colour and integrates the lettering
with the imagecorrespond perfectly to the strengths of lithography,
making it an ideal medium for printing posters.
Lithographs
are drawn with a greasy crayon on a prepared Kelheim stone (though
due to the increasing rarity of this dense limestone, prepared plates
of zinc or aluminium can be used instead). The stone is treated
with nitric acid and water, and then gum arabic is applied. When
the stone is dampened with water, ink will only adhere to the design.
The inked stone and paper are then run through a printing press
and the design is transferred onto the paper. Colour or chromolithographs
are produced using a different stone for each colour.
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