Indentation hardness
Hardness measurements quantify the resistance of a material to plastic deformation. Indentation hardness tests compose the majority of processes used to determine material hardness, and can be divided into two classes: "microindentation" and "macroindentation" tests. Microindentation tests typically have forces less than . Hardness, however, cannot be considered to be a fundamental material property. Classical hardness testing usually creates a number which can be used to provide a relative idea of material properties. As such, hardness can only offer a comparative idea of the material's resistance to plastic deformation since different hardness techniques have different scales.
Hot hardness
In materials engineering and metallurgy, hot hardness or red hardness (when a metal glows a dull red from the heat) corresponds to hardness of a material at high temperatures. As the temperature of material increases, hardness decreases and at some point a drastic change in hardness occurs. The hardness at this point is termed the "hot" or "red" hardness of that material. Such changes can be seen in materials such as heat treated alloys.