The Dampening System

The dampening system applies a aqueous dampening solution to the plate before it is inked. This keeps the nonimage area moistened to that it will not accept ink.

Gum in the fountain solution adsorbs on the nonimage area to keep it water-wet. The gum does not adsorb on the image area which is not water-wet. This area is generally oil-wet.

A concentrated form used to mix a fountain solution is called fountain concentrate, fountain etch or just etch. These usually contain Gum Arabic or synthetic gums for desensitizing.

Most dampening solutions are acidic (pH 4-5) because the gum performs best under acid conditions. Recall that the gum reacts with and attaches to the Aluminum oxide surface of the plate.

Other material contained in dampening solution are

1) corrosion inhibitors to prevent reactions with the plate,

2) a pH buffer, wetting agents such as isopropanol or its substitutes,

3) a fungicide to prevent mildew and the growth of fungus and bacteria in the dampening system, and

4) an antifoaming agent facilitate even distribution of dampening solution. Some concentrates may require added alcohol in addition to water.

Water - The effectiveness of dampening solution depends on local water supply. Hard water requires stronger acid than soft.

To assure the most consistent performance, use distilled or deionized water. The plate wetting characteristics depend on surface tension of dampening solution.

This is reduced by both the gum (surfactant) and the alcohol (cosurfactant). The alcohol also increases the viscosity of the dampening solution which allows a thicker layer of dampening solution to be applied to the nonimage area of the plate.

The alcohol evaporates faster than water so that less dampening solution reaches the paper. The alcohol reduces the tendency of ink to emulsify into the dampening solution.