The gloss on a surface is assessed by its reflection properties.

Although the eye also considers the mirror (picture) effect gloss remains essentially a matter of reflection. The reflection effect will depend on the angle at which the surface is viewed. To measure gloss using a so-called gloss scale, reflected light applied at specified angles is measured.

The range of categories of gloss has been divided into high gloss, medium gloss and matt and for each of these different measuring geometries have become established. The measured gloss is expressed by a number in the relevant category, thus providing an accepted method of communication.