342 JOURNAL OF COSMETIC SCIENCE 250 2OO •0150 E Natural White Light Blonde Light Brown Dark Brown i i i i 0 10 20 30 40 Distance (rnrn) Figure 7. Light intensity (luminance) as a function of distance along the hair tress for various types of hair. extent of fiber pigmentation, which indicates that it is due to reflection from the back face of the hair fibers. The narrowest light distribution curve was obtained, as expected, for dark brown hair. Hair luster parameters, calculated according to equations 2 and 3, are presented in Table I. The calculations carried out by both formulas indicate lower luster values for fibers containing less melanin pigment, i.e., the highest luster for dark brown hair and the lowest for natural white hair. A similar result was previously reported by Stammet (2). Also, W•/2 follows the same trend, consistent with visual perception, pointing to an increase in the width of reflected light distribution for less pigmented fibers. MEASUREMENTS OF OIL-TREATED HAIR We have performed a series of measurements on hair treated with silicone oils including phenyl trimethicone and amodimethicone as well as with the hydrocarbon oil and castor oil. The structures of these cosmetic raw materials are shown below (Schemes 1-2). Castor oil consists of triglycerides of fatty acids with the predominant presence of ricinoleic acid residues (97%) (Scheme 3). Table I Luster Parameters for Various Hair Types (f8 1/13 s) Hair type W•/2 (mm) Ls ...... LR,,,3 teob•,,, Dark brown 5.28 _+ 0.44 0.72 + 0.020 0.67 + 0.006 Medium brown 5.44 + 0.16 0.72 + 0.006 0.67 + 0.005 Light brown 10.46 + 0.30 0.70 + 0.001 0.32 + 0.008 Light blonde 14.91 + 0.23 0.65 + 0.005 0.19 _+ 0.006 Natural white 22.78 + 0.24 0.32 _+ 0.013 0.06 + 0.002

LUSTER QUANTIFICATION OF HAIR 343 ll3 H3C•S i CH3 O CH 3 ll3 Si--O CH• Si Si(CH3)3 Scheme 1. Phenyl trimethicone. (i H2)3 NH(CH2)2NH2 Scheme 2. Amodimethicone. HO•C17H32'COOH Scheme 3. Ricinoleic acid. CH 3 ll3 CH 3 CH 3 Phenyl trimethicone is commonly used in leave-in cosmetic formulations as a shining agent. Amodimethicone, on the other hand, is typically employed in rinse-off condi- tioners as a conditioning agent effective in reducing combing forces. Castor oil usually plays the role of a texture modifier and conditioner in a variety of cosmetic products. Figure 8 provides the images obtained for dark brown hair treated with phenyl tri- methicone, amodimethicone, and castor oil, which were applied at 2% concentration in ethanol. It is apparent that all three materials modify the contrast between specular reflection and other regions of the tress. As a result of treatment with these oils, one can observe a lightening effect in the region of the tress immediately adjacent to the specular reflection and darkening of the area further away from the specular band, located in the regions corresponding to 0-10 mm and 35-50 mm, respectively (compare with Figure 9, which provides the distance scale for the images shown in Figure 8). The lightening effect (or broadening of specular reflection) is most evident in the case of castor oil but is also clearly visible for phenyl trimethicone-treated hair. A graph of luminance as a function of tress length for phenyl trimethicone is presented in Figure 9. The broadening of the specular band takes the form of a left-hand-side shoulder in the