Gloss (optics)

Gloss is an optical property which indicates how well a surface reflects light in a specular (mirror-like) direction.

Other categories of visual appearance related to the perception of regular or diffuse reflection and transmission of light have been organized under the concept of cesia in an order system with three variables, including gloss among the involved aspects.

The factors that affect gloss are the refractive index of the material, the angle of incident light and the surface texture.

When light illuminates an object, it interacts with it in a number of ways: Variations in surface texture directly influence the level of specular reflection.

The image forming qualities of these surfaces are much lower making any reflections appear blurred and distorted.

Metals do not suffer from this effect producing higher amounts of reflection at any angle.

The path difference between rays reflected from the top and bottom of the surface bumps is: When the wavelength of the light is

is small, the two beams (see Figure 1) are nearly in phase, resulting in constructive interference; therefore, the specimen surface can be considered smooth.

, then substitution into the equation above will produce: This smooth surface condition is known as the Rayleigh roughness criterion.

Using this configuration gloss was measured using a contrast method which subtracted the specular component from the total reflectance using a polarizing filter.

In the 1930s work by A. H. Pfund,[3] suggested that although specular shininess is the basic (objective) evidence of gloss, actual surface glossy appearance (subjective) relates to the contrast between specular shininess and the diffuse light of the surrounding surface area (now called "contrast gloss" or "luster").

In his paper Hunter also noted the importance of three main factors in the measurement of gloss: For his research he used a glossmeter with a specular angle of 45° as did most of the first photoelectric methods of that type, later studies however by Hunter and D. B. Judd in 1939,[5] on a larger number of painted samples, concluded that the 60 degree geometry was the best angle to use so as to provide the closest correlation to a visual observation.

[non-primary source needed] 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.

ASTM has a number of other gloss-related standards designed for application in specific industries including the old 45° method which is used primarily now used for glazed ceramics, polyethylene and other plastic films.

In the paint industry, measurements of the specular gloss are made according to International Standard ISO 2813 (BS 3900, Part 5, UK; DIN 67530, Germany; NFT 30-064, France; AS 1580, Australia; JIS Z8741, Japan, are also equivalent).

Studies of polished metal surfaces and anodised aluminium automotive trim in the 1960s by Tingle,[7][8] Potter and George led to the standardisation of gloss measurement of high gloss surfaces by goniophotometry under the designation ASTM E430.

In this standard it also defined methods for the measurement of distinctness of image gloss and reflection haze.