The dampening system on a lithographic sheet fed press applies a water-based dampening or fountain solution to the printing plate before it is inked. Dampening solutions keep the non-image areas of a plate moistened so that they will not accept ink, and are applied to the entire plate.The non-image areas of the plate, which are made that way by adsorbing a thin film of gum Arabic to them during plate making, are hydrophilic (water loving) while the image areas are hydrophobic (water repellent). The desensitizing film on the non-image areas wears off gradually as the plate continues to run on press, so the chemicals in the dampening solution replenish the desensitizing film. Ink, plate, press speed, paper, temperature, and relative humidity are the principal factors that influence the need for various dampening solutions.