A device (also called a type-A durometer) used to measure the hardness of the surface of an offset printing ink roller, offset blanket, or gravure impression roller, and the term for the roller or blanket's hardness itself. Durometer is measured on a scale of 0 to 100, where 0 is an extremely flexible surface, and 100 is an extremely inflexible surface, such as cast iron. A roller's surface (i.e., the compound—such as rubber—that comprises its surface) must maintain a certain degree of flexibility and resilience in order to effect proper ink transfer. However, the required hardness or softness depends on the specific type of ink roller (i.e., a form roller, oscillator, etc.); a form roller should have a more resilient surface (thus a lower durometer) than a distributor, for example. A roller's durometer increases with age, as exposure to such things as light, heat, solvents, and so on, cause chemical reactions in the surface compound, causing a progressive hardening and shrinking. Glazing is also a common cause of roller hardening. An increase of 10:15 durometer points is common over the course of a roller's lifetime, but increases beyond that cause a degradation of ink transfer and print quality. (See also Type-A Durometer, and Impression Roller.)
The flexibility of a squeegee blade used in screen printing is also measured in terms of durometer.