All about a glossmeter- In detail

Glossmeter

What is a Glossmeter?

glossmeter (also gloss meter) is an instrument which is used to measure the specular reflection (gloss) of a surface.  Gloss is determined by projecting a beam of light at a fixed intensity and angle onto a surface and measuring the amount of reflected light at an equal but opposite angle.

There are a number of different geometries available for gloss measurement, each being dependent on the type of surface to be measured.  For non-metals such as coatings and plastics the amount of reflected light increases with a greater angle of illumination, as some of the light penetrates the surface material and is absorbed into it or diffusely scattered from it depending on its colour.  Metals have a much higher reflection and are therefore less angularly dependent.

Many international technical standards are available that define the method of use and specifications for different types of glossmeter used on various types of materials including paint, ceramics, paper, metals and plastics.  Many industries use glossmeters in their quality control to measure the gloss of products to ensure consistency in their manufacturing processes.  The automotive industry is a major user of the glossmeter, with applications extending from the factory floor to the repair shop.

History of a Glossmeter

Of the many internationally recorded publications relating to gloss measurement, the earliest recorded studies (perceived and instrumental) are attributed to Ingersoll1 who in 1914 developed a means to measure the glare of paper.  The Ingersoll “Glarimeter”, the earliest known instrument developed for gloss measurement, was based on the principle that light is polarised in specular reflection.  The instrument employed incident and viewing angles of 57.5° and used a contrast method to subtract the specular component from the total reflection using a polarising element.  Ingersoll successfully applied for and patented this instrument a few years later in 1917.

In 1922 Jones2, during his study of gloss of photographic papers using goniophotometry, developed a glossmeter based on his research, which provided closer correlation to gloss ratings assigned by visual evaluation.  Jones’ glossmeter used a geometric configuration of 45°/0°/45° whereby the surface was illuminated at 45° and two incident reflective angles measured and compared at 0° (diffuse reflectance) and 45° (diffuse plus specular reflectance).  Jones was the first to emphasize the importance of using goniophotometric measurements in studies of gloss.

Early work in 1925 by Pfund3 led to the development of a variable angle “glossimeter” to measure specular gloss which was later patented in 1932.  Pfund’s instrument, allowed the angle of measurement to be varied, but maintained the angle of view to the angle of illumination. Reflected light was measured using a pyrometer lamp as a photometer.  The ‘glossimeter’ was the first to use black glass standards as a basis for reflectance setting.  As the angle was variable this instrument could also be used for the measurement of sheen or specular gloss at near grazing angles.

During this time, growing interest in this field resulted in a number of similar studies by other individuals each having their own method for gloss measurement, most of which published as technical articles in scientific journals of that time.  A few of these also resulted in patents.

In 1937 Hunter, as part of a research project for the US National Bureau of Standards, produced a paper on the methods of determining gloss. In this paper he discussed instruments that were available at the time (including the ones mentioned previously) in relation to the classification of six different types of gloss.  In this paper Hunter also detailed the general requirements for a standardised glossmeter.

Standardisation in gloss measurement was led by Hunter and ASTM (American Society for Testing and Materials) who produced ASTM D523 Standard test method for specular gloss in 1939.  This incorporated a method for measuring gloss at a specular angle of 60°. Later editions of the Standard (1951) included methods for measuring at 20° (high gloss) and 85° (matt, or low, gloss).  ASTM has a number of other gloss-related standards designed for application in specific industries.

In the paint industry, measurements of specular gloss are made according to International Standard ISO 2813.  This standard is nominally the same as ASTM D523 although differently drafted.  BS 3900, Part 5, UK; DIN 67530, Germany; NFT 30-064, France; AS 1580, Australia; JIS Z8741, Japan, are also equivalent.