GLOSS OF HAIR SURFACES - PROBLEMS OF VISUAL EVALUATION AND POSSIBILITIES FOR GONIOPHOTOMETRIC MEASUREMENTS OF TREATED STRANDS

A great number of products are offered on the hair cosmetics market th at, in addition to their basic benefit, aim to improve hair gloss. Glo ss can be regarded as a special optical property for the description o f apparent decorative qualities and for the analysis of surface proper ties of hair. As it is very complex, no simple relationship exists bet ween the appearance of gloss and the light reflected from the hair. Bu t up to now, investigations made on various materials suggest the spat ial distribution of reflected light, the indicatrix, as being very imp ortant. Therefore, hair indicatrices were measured using a precise gon iophotometer. The resulting data had to be compressed, both for easier handling and for the description of significant aspects of the visual gloss impression. Two indicatrix parameters are regarded as ''gloss c riteria'': the improvement of gloss is related to an increasing amount of maximal reflected light and a decreasing half-value angle, which m eans the spread of reflected light in different angular directions. Th e reproducibility and the precision of these measurements required an air-conditioned test room, an optimized preparation technique includin g the construction of a special sample holder for the hair strands, an d the minimizing of the variance between the strands by always compari ng the indicatrices of the untreated and the treated samples. The stra nds were treated with various hair cosmetics, e.g., hair sprays, lacqu ers, rinses, care sprays, as well as glazes and hair gels. To check th e correlations between the results of the objective measurements and t he visual gloss inspection, several gloss evaluations were made in a ' 'gloss matching booth.''