Gloss (material Appearance)

Gloss (material Appearance)

Gloss is an optical property describing the ability of a surface to reflect light into the specular direction. The factors that affect gloss are the refractive index of the material, the angle of incident light and the surface topography.

Gloss is one of the factors that describe the visual appearance of an object. Materials with smooth surfaces appear glossy. Very rough surfaces such as chalk reflect no specular light and appear dull. Gloss is also expressed as lustre in mineralogy, or sheen in certain fields of application.

The appearance of gloss depends on a number of parameters which include the illumination angle, surface condition and observer characteristics.

Primarily light is reflected from a surface in one of two ways. In specular reflection, the angle of the light reflected from the surface is equal and opposite to the angle of the incident light. A diffuse reflection scatters the incident light over a range of directions.

Variations in surface texture influence specular reflectance levels. Objects with a fine surface texture, i.e. highly polished and smooth, allow a high percentage of light to be reflected from their surfaces making them appear shiny to the eye. This is due to a greater amount of incident light striking the surface being reflected directly back to the observer; the majority of which being reflected in the specular direction.

Conversely objects with rough surfaces cause the light to be deflected at different angles according to the surface profile resulting in a scattering of light away from the angle of reflection. This causes the object to appear dull or matte. The image forming qualities are much lower making any reflection appear blurred. The higher the degree of surface roughness, the greater the scattering of light resulting in a lower gloss level.

Equally the type of substrate material has an important effect on the amount of specular reflection from its surface. Nonmetallic materials, i.e. plastics / coatings, 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 than nonmetals.