A Shearling Coat

Specular reflection, gloss, roughness and surface heterogeneity of biopolymer coatings

“…12,14 The effect of specular gloss is clearly seen with mirrors and polished metal surfaces. 9 Although specular gloss can be described mathematically and measured quantitatively, it cannot account for all of the light-reflecting properties of a surface. There is no single equation that can calculate all types of gloss, or a single instrument that can measure all types.…”

“…15 Specular reflectance is defined as the ratio of the intensity of the reflected beam to the intensity of the incident beam of light at a specific angle of incidence. 9,11 Specular reflectance is a function of refractive index of the surface (n), the extinction index (k), the angle of incidence of the beam of light (), and the nature of the reflecting light. 16 The quantities n and k are referred to as the optical constants of the material.…”

“…Typically, unpolarized light is used for gloss measurements. 16,20 For unpolarized light, the total reflectance (R) is calculated as the average of the parallel and perpendicularly polarized beams 9,16,20 :…”

“…A rough surface will have a large effect on the amount of light that is specularly reflected from that surface. 9 To determine the roughness in practical systems, a model was developed that assumed a randomly rough surface on which the distribution of surface defect heights was normally distributed. 14 The roughness can then be determined from the reflectance of the sample from the following expression 9,14,25,27 :…”

“…This expression is sometimes referred to as the Bennet-Porteus model. 9 Here R is the sample reflectance of a rough surface, R o is the reflectance from an optically smooth surface of the same material, and is the root-mean-square roughness (nm). R o , which is the same value as R unpolarized for the optically smooth surface, is typically calculated from eqs.…”