A metal roller found in the ink fountain on a printing press used in offset lithography. The fountain roller is in direct contact with the ink from the fountain, the amount of ink transferred to it being regulated by the gap between the roller and the fountain blade. The fountain keys adjust the width of this gap, allowing more or less ink to transfer to the fountain roller. Contacting the fountain roller at set intervals is the ductor roller, which transfers ink from the fountain roller to the rest of the ink roller train and, ultimately, to the plate. The fountain roller can rotate at varying rates, depending upon how much ink is ultimately required by the plate. A fountain roller that turns through a longer distance will transfer more ink to the surface of the ductor roller, and a longer amount of contact between the ductor and fountain rollers (called dwell) also affects how much ink is sent through the system. The best results can generally be obtained by allowing the fountain roller to have a long sweep—or turn through a longer distance—but a thin ink film. This allows a greater sensitivity of the rest of the system to ink flow adjustments made with the fountain keys. (See Inking System: Offset Lithography and Offset Lithography.)
A fountain roller is also used in some gravure inking systems. A gravure fountain roller is an absorbent roller that absorbs ink from the bottom of a shallow ink fountain and squeezes it into the engraved cells of the gravure cylinder rotating above it. (See Inking System: Gravure.)
A fountain roller is also used in many flexographic ink fountains, typically having a natural or synthetic rubber surface that transfers ink to the surface of an anilox roller. A fountain roller used in flexography is also known as a doctor roller. See Inking System: Flexography.