Gloss is a measure of how reflective a material is at a specified angle based on refractive index.
A gloss meter comprises an incandescent light source which is directed at the test surface at a specified incidence angle and a receptor which is located at the mirror reflection of the incident beam. A polished black glass with a refractive index of 1.567 is used as a standard and is assigned a gloss of 100 at all geometries.
Gloss readings can only be compared between similar materials and test procedures. For example, gloss values for transparent and opaque materials are not comparable. Gloss varies with smoothness and flatness and is sometimes used to compare attributes of pearlised OPP films.
A low 20º viewing angle is used for evaluating high gloss films, a 45º angle for intermediate gloss films and a 60º or an 85º angle for low gloss films. Gloss values increase with increasing angle when the same film is tested.
Standards and Accreditation
There are a number of standards we can test to, including:
- ASTM D523 covers the measurement of the specular gloss of non-metallic specimens for gloss meter geometries of 20, 60, and 85°.
- ASTM D2457 describes procedures for the measurement of gloss of plastic films and solid plastics, both opaque and transparent at 20, 45, 60, and 75°.
- ASTM C346 for 45º specular gloss of measurement of ceramic materials.
- BS 2782:520A - Determination of specular gloss using 20, 60 and 85º gloss devices, also with a matt backing.
- ISO 2813 - Determination of specular gloss of non-metallic paint films at 20, 60 and 85º angles.