Hardness Hardness Hardness is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. Some materials (e.g. metals) are harder than others (e.g. plastics, wood). Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore, there are different measurements of hardness: "scratch hardness", "indentation hardness", and "rebound hardness". Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity. Common examples of hard matter are ceramics, concrete, certain metals, and superhard materials, which can be contrasted with soft matter. There are three
Draize test are removed with sticky tape), then covered with plastic sheeting. According to the British Research Defence Society, the Draize eye test is now a "very mild test," in which small amounts of substances are used and are washed out of the eye at the first sign of irritation. In a letter to "Nature", written to refute an article saying that the Draize test had not changed much since the 1940s, Andrew Huxley wrote: "A substance expected from its chemical nature to be seriously painful must not be tested in this way; the test is permissible only if the substance has