The visual evaluation of the gloss of a surface is a complex interaction between the observer’s eye and the surface of the object. This process depends on a number of psychophysical factors that can affect visual perception including age, gender, mood and day of the week amongst others. Therefore it is quite common for a group of individuals to produce large variations in results when describing the gloss of a surface.
When light illuminates an object, it interacts with it in a number of ways:
Absorbed within it (largely responsible for colour)
Transmitted though it (dependent on the surface transparency and opacity)
Scattered from or within it (diffuse reflection, haze and transmission)
Specularly reflected from it (gloss)
Variations in surface texture directly influence the level of specular reflection. Objects with a smooth surface, i.e. highly polished or containing coatings with finely dispersed pigments, appear shiny to the eye due to a large amount of light being reflected in a specular direction whilst rough surfaces reflect no specular light as the light is scattered in other directions and therefore appears dull. The image forming qualities of these surfaces are much lower making any reflections appear blurred and distorted.
Substrate material type also influences the gloss of a surface. Non-metallic materials, i.e. plastics etc. produce a higher level of reflected light when illuminated at a greater illumination angle due to light being absorbed into the material or being diffusely scattered depending on the colour of the material. Metals do not suffer from this effect producing higher amounts of reflection at any angle.