Glossmeter

glossmeter

A glossmeter is an instrument which is used to measure gloss of materials such as paint, plastics and paper. Gloss is a measure of the proportion of light that has a specular reflection from the surface. A surface such as a mirror has a high gloss, where a surface such as chalk has less because the light reflected is diffused. Numerous international technical standards define the method of use and specifications of different types of glossmeter used on different types of materials.

Measurement

Specular and diffuse reflection

The glossmeter provides a quantifiable way of measuring gloss intensity ensuring consistency of measurement by defining the precise illumination and viewing conditions. The configuration of both illumination source and observation reception angles allows measurement over a small range of the overall reflection angle. The measurement results of a glossmeter are related to the amount of reflected light from a black glass standard with a defined refractive index. The ratio of reflected to incident light for the specimen, compared to the ratio for the gloss standard, is recorded as gloss units.

Three measurement angles are specified to cover the majority of industrial coatings applications. The angle is selected for a particular application based on the anticipated gloss range.

Gloss Range	60° Value	Angle
High Gloss	>70 GU	20°
Medium Gloss	10 - 70 GU	60°
Low Gloss	<10 GU	85°

For example if the measurement made at 60° is greater than 70 GU the measurement angle should be changed to 20° to optimise measurement accuracy.

Two further angles are used for other materials. The 45° angle is specified for the measurement of ceramics, films, textiles and anodised aluminium whilst the 75° angle is specified for paper and printed materials.

Gloss units

The measurement scale, Gloss Units (GU), of a glossmeter is a scaling based on a highly polished reference black glass standard with a defined refractive index having a specular reflectance of 100GU at the specified angle. This standard is used to establish an upper point calibration of 100 with the lower end point established at 0 on a perfectly matt surface. This scaling is suitable for most non-metallic coatings and materials (paints and plastics) as they generally fall within this range. For other materials, highly reflective in appearance (mirrors, plated / raw metal components), higher values can be achieved reaching 2000 Gloss Units. For transparent materials, these values can also be increased due to multiple reflections within the material. For these applications it is common to use % reflection of incident light rather than Gloss Units.

Standards

Comparision of standards for gloss measurement

Standard	20°	60°	85°	45°	75°
	Low Gloss	Medium Gloss	High Gloss	Medium Gloss	Low Gloss
	Coatings, plastics and related materials			Ceramics	Paper
ASTM C346				X
ASTM D523	X	X	X
ASTM C584		X
ASTM D2457	X	X		X
BS3900 D5	X	X	X
DIN 67530	X	X	X
DIN EN ISO 2813	X	X	X
EN ISO 7668	X	X	X	X
JI Z 8741	X	X	X	X	X
TAPPI T480					X

See also

• Gloss (paint)
• Drawdown card
• Distinctness of image

External links

• Rhopoint Instruments
• Description from gloss-meters.com
• ISO 2813:1994 Paints and varnishes -- Determination of specular gloss of non-metallic paint films at 20 degrees, 60 degrees and 85 degrees
• http://www.byk.com/en/iinstruments/appearance/gloss/micro-gloss.html
• http://malaysia.answers.yahoo.com/question/index?qid=20060630091429AAZlIgC