To materials engineers and technologists, gloss is a property of surfaces which causes them to have a shiny or mirrorlike appearance. This appearance cannot be measured; only specific reflectance capacities of surfaces can be measured. Although gloss may be associated with the capacity of a surface to reflect like a mirror, there is no single reflectance scale yielding values that correlate with the glossy appearance of all surfaces. This is because the capacities of surfaces to reflect light in and adjacent to the directions of mirror reflection are too complex and varied to be compared on any single scale. As a consequence, different gloss scales involving different geometric aspects of light reflectance have been developed. Each provides numbers correlating with the glossy appearance of the specific types of surfaces to which it is applicable. For certain types of glossy appearance, however, correlating methods of reflectance measurement do not exist.