Silkiness in brown mink pelts characterized with optical methods

In mink production, silkiness refers to a silky fur surface. The sensory evaluation of silkiness may be based on information perceived by the eyes and the hands. Silkiness is assumed to depend on hair fiber properties such as guard hair straightness, glossiness, and smoothness. Our objective was to characterize the dorsal surface of brown mink pelts by means of optical variables and relate these to the visual grades of silkiness, thereby forming some objective criteria of silkiness. Two groups of brown male mink pelts (winter coat) that originated from a selection trial with a focus on silkiness were used. The pelts came from a basic (Group 1992) population and a selected (Group 1994) generation. Group 1992 was graded visually on a scale from 1 to 6 (most silky); Group 1994 was graded on a scale from 1 to 8 (most silky). With goniophotometric, nondestructive methods, the reflectance from each pelt surface was measured describing the angle-dependent distribution of reflection in the shape of angular reflectance curves. The measurements were performed along (w-reflectance curve) and across (c-reflectance curve) the guard hairs. The w-curve included a maximum assumed to be related to silkiness. Specular gloss, indicated by the maximum reflectance (s) in the direction of mirror reflection, was positively correlated with silkiness. For Group 1994, s = 72.94 + .49 x silkiness; r2 = .33, P = .0003. Correspondingly, an area representing specular (S) plus diffuse (D) reflectance (S + D) under the curve was positively correlated with silkiness. A decreasing band width of the w-curve at 90% of maximum specular reflectance (w90) was related to an increase of silkiness (Group 1992: r = -.50, P < .01). Furthermore, both s/w90 and (S + D)/w90 were positively correlated with silkiness (Group 1992: r = .49, P < .01 and r = .51, P < .01, respectively). Measures of contrast gloss involving relations or differences between specular and diffuse reflectance were not suitable. From our results, a high degree of specular gloss, indicated by s, explained and was related to an essential part of silkiness and general sensory quality of the pelts investigated. Also, s was relatively easy to measure. Thus, even if the objective variables did not correlate perfectly with visual judgments, s was considered to be the most usable objective variable in characterizing silkiness.