is the techniques of applying ink to paper or
other substrates. There are five basic printing methods: letterpress,
flexography, gravure, lithography, and screen. Letterpress and
flexography both use inked raised type on plates wrapped around a
rotating cylinder. Flexography differs from letterpress in that the plate is
flexible rubber, rather than metal. The two processes are used where print
quality is not a primary consideration, such as newspapers, phonebooks,
paper bags, and cardboard packaging. Gravure, or intaglio, printing
employs an etched or engraved plate that holds ink in tiny cells (thousands
per square inch) below the plate surface. This technique produces the
highest quality print and is preferred for photo reproduction.
Lithography, or planography, uses a smooth plate created by a
combination of photochemical and photomechanical processes that make the
printing area ink receptive and the non-printing area water receptive.
Lithography is also called offset printing because the image is
transferred from the plate to a rubber roller or blanket, which prints the
image. Lithography is gradually replacing letterpress in newspaper and
magazine printing. Screen printing uses a porous screen and a stencil
that covers the non-printing areas. Ink is forced through the stencil
openings onto the substrate. Screen printing is commonly used wherever a
thick, durable ink coating is desired, such as T-shirts and outdoor posters.
Petroleum-base ink solvents are commonly used
in formulating the ink used in these various processes.
Also see printing ink,
printing ink solvent,
tack.