micro-gloss and samples. Photo Courtesy of BYK-Gardner.

Gloss

Gloss is an optical phenomenon caused when evaluating the appearance of a surface. The evaluation of gloss describes the capability of a surface to reflect directed light. A gloss meter measures the specular reflection. The intensity of the reflected light is dependent on the material and the angle of the illumination. In order to obtain a clear differentiation over the complete measurement range from high gloss to matte, 3 geometries (ranges) were defined.

The three angles defined to measure gloss.
Photo Courtesy of BYK-Gardner.

Gloss Angles

Using the 60º gloss angle as a reference angle, the working range for 60º gloss is 10-70 GU (gloss units). This is considered the Semi Gloss range. Below 10 GU or above 70 GU, the 60º gloss measurement does not correlate with a visual assessment of gloss. Therefore for measurements above 70 GU, the 20º glossmeter is used for High Gloss surfaces. For below 10 GU, the 85º glossmeter is used. This is referred to as Low Gloss or Matte.

Graph of 13 ranked gloss samples and their measured gloss values in gloss units (GU). Below 10 GU and above 70 GU, the 60° curve is flat and the differences can no longer be seen. One must switch to either 85° or 20°.
Photo Courtesy of BYK-Gardner.

There are also two additional angles, 45º and 75º. These angles are industry specific for measuring paper and plastic films.

Chart showing when to use each gloss angle.
Photo Courtesy of BYK-Gardner.