88 JOURNAL OF COSMETIC SCIENCE The data given in Table I represent the accepted data for the gloss index and are arithmetic means for measurements taken at a given position relative to the root end on a number of hairs (N) of the same type. For a given hair type the data are summarized in group means. Data are further summarized over all hair types in the form of a grand mean. Effects of measurement position and hair type on the parameters were assessed for significance by analysis of variance (ANOV A) and linear regression (LR). In those cases where ANOVA indicated inhomogeneity, multiple comparison of means analysis was conducted, applying the nonconservative LSD test (21). Statistical significance of effects (ANOV A: inhomogeneity of data LSD: differences between data groups LR: slope of the regression line) is characterized throughout by the a-value (22), which is the probability of committing a so-called Type I error, i.e., by finding an effect that in fact does not exist. In cases where a 0.05, effects are significant at the usual 95% level and beyond. The results for the three hair types are summarized in Figure 3 in the form of a box-and-whisker plot. Analysis of variance shows that, in agreement with the visual impression, the data are inhomogeneous well beyond the 95% level (a 0.0001), where the LSD test identifies the a-levels for the differences, as given on the horizontal whiskers in Figure 3. Here it is shown that the gloss index shows no significant difference between black and brown, but is decreased rather dramatically for the blonde hair. This effect can be largely attributed to the absorption of refracted light for the two dark hair types, which suppresses diffuse light reflection from the hair interior and thus induces a strong and brilliant hair luster. Table I Values for the Gloss Index G L Derived from the GP Curves for Various Hair Types Hair type Black Group mean ± q Brown Group mean ± q Blonde Group mean ± q Grand mean ± q Position (cm) 1 5 10 15 20 10 20 25 30 1 5 10 15 20 N CL(%) 12 64.1 3 53.2 7 59.3 3 59.8 7 57.4 32 60.2 ± 3.33 10 66.5 9 54.4 7 55.8 4 55.6 10 57.6 40 58.6 ± 3.05 10 31.8 9 32.2 9 30.7 9 14.9 10 14.7 47 24.8 ± 3.84 119 45.7 ± 3.66 A number of hairs (N) were measured at various positions relative co the root. Group and grand mean values are given with their 95% confidence range ± q.
70 60 ,c 50 a, MEASURE OF HAIR LUSTER ..................... ,____1 -----.---f ____, ....... -·,____I --� ____,1 ··. 0.001 : 40 ........................... _________________ _ 0 CJ 30 20 Mean D Std.Err. I 95% Conf.Rg. black brown Hair Type blonde 89 Figure 3. Box-and-whisker plot summarizing gloss index values for the three hair types. Data points, boxes, and whiskers are defined by their arithmetic group mean (Mean), the standard error (Std. Err.), and the limiting value for the 95% confidence range (95% Conf. Rg). The horizontal whiskers signify a specific comparison of means (LSD test), given with the a-value to characterize the significance of the difference. There are changes in the gloss index along the hair length, as summarized graphically in Figure 4. Each straight line represents a fit to the mean values given. Considerations of statistical significance relate, however, to fits of the single data. For the black hair, the change of gloss along the hair length is a tendency at best, but in fact not significant at the chosen 95% significance level (a = 0.2). The level of the grand mean for the gloss index of the black hair is marked in Figure 4. For the brown hair, the decrease of gloss along the hair length is more pronounced and the significance of the slope of the regression line just misses the 95% level (a = 0.054). For the blonde hair, gloss starts from an already comparatively low level at the root and then decreases strongly and significantly towards the tip (a 0.001). The decrease in hair gloss due to a relative increase in the intensity of diffusely reflected light can be attributed to hair color lightening towards the fiber tip combined with the formation of damage-related structures, such as cracks or voids, that scatter light, which have been induced by daily hair grooming practices including heat treatments (20,23), sunlight exposure, etc. Black and brown hair reach values around 65% gloss near the root ends, which may be considered a reasonable estimate for the maximum natural gloss of hair. For natural black or dark brown hair, diffuse reflection from the fiber interior will be negligible due to the absorption of the refracted light. However, for all hair types, cuticle
Previous Page Next Page