Such drying can he accellerated by blowing hot or cold air over the surface to be dried. This is the case with oil paint and glycerophtalic inks. The oxydation process, as opposed to penetration which is a physical process, is nothing less than a chemical reaction of the ink with oxygen. The oxygen coming into contact with these inks brings about polymerization and therefore a progressive thickening of the ink until it reaches its final, hard stage. The drying agent used accellerates the oxydation process.
Heat helps to activate drying processes depending on oxydation.
Photogravure inks dry by evaporation and by penetration. With cellulose and ethylcellulose base inks, fluorescent inks as well as some synthetic inks and some water base inks, drying is achieved by evaporation and penetration. Clycerophtalic inks dry by oxydation after the evaporation of the solvent they contain. Different inks have different drying times. Typographical inks are fast drying for machine printing and medium fast drying for manual impressions.