Each printing process requires the use of an ink developed specifically for that process. Letterpress, gravure, lithographic, and screen-process inks are specially formulated to match the requirements of the printing process. For example, letterpress inks are designed to distribute evenly over and adhere well to raised plate surfaces. Gravure inks are quite fluid and dry rapidly.
Lithographic inks are formulated so as not to absorb or combine with the fountain solution in the press. And inks used for screen-process printing will have the consistency of thick paint, which is usually required in this process.
Another consideration when selecting an ink is the eventual use of the printed item. For example, ink on items used outdoors must be able to withstand the weather. Ink printed on fabrics should hold up under repeated washings. Food packages should be printed with an odorless ink. And products that will be handled by young children must be printed with non-toxic inks.