Flexography is one method of printing words and images onto foil, plastic film, corrugated board, paper, paperboard, cellophane, or even fabric. In fact, since the flexographic process can be used to print on such a wide variety of materials, it is often the best graphic arts reproduction process for package printing. Flexography is related to the oldest printing process, letterpress, because both flexography and letterpress print from a raised image. In its original form, letterpress used individual metal characters called types and a mechanical press. The type was combined to form words and sentences and tightly arranged on the flat surface of the press. Then the raised areas were covered with ink. The message was formed when paper was pressed against the flat metal type. To speed up the slow process of pressing flat surfaces together, the printing press evolved from printing on a flat surface only to using a rolling cylinder, as with this cylinder press on the left. The type moved back and forth between inking rollers and an impression cylinder, which held the paper. To help meet the growing demand for printed products, printing from inked type soon moved to printing from an inked plate. Rotary letterpress prints from a molded or etched metal plate like the one on the right. Flexography prints from a flexible printing plate that is wrapped around a rotating cylinder. The plate is usually made of natural or synthetic rubber or a photosensitive plastic material called photopolymer. It is usually attached to the plate cylinder with double-sided sticky tape. Flexography was first called aniline printing because early flexographic inks contained dyes derived from aniline oil–a liquid extracted from the indigo plant. These dyes were dissolved in spirits, making a quick-drying ink. The combination of a flexible plate, quick-drying ink, and the ability to print on such a wide variety of materials or substrates made this process excellent for package printing.