printing processes - 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 letter press 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 pack aging. 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 news paper 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. See printing ink, printing ink solvent, tack.