HAIR APPEARANCE AND INTERNAL STRUCTURE 393 clarify the influence of the porous structure in the hair fiber. A visual image of the poreless hair and the hair with a porous medulla are shown in Figure 4, as typical examples. The members of the panel expressed that the poreless hair looked lustrous and colorful and gave an impression of depth along transparency. On the other hand, the hair with a porous medulla was seen by the panelists as lusterless, white-chalky, dull, dry, and flat. In the case of the hair with micropores in the cortex, the expressions were similar or more negative, compared to the hair with the porous medulla. The evaluation of the hair samples was charged from positive to negative in the following order: poreless porous medulla = pores in cortex, in the present case. The order of the evaluation corresponds to the order of the goniophotometric data in Figure 3. The poreless hair in Figure 4 actually shows an intensive highlight zone by the specular reflection from the front surface, a brilliant and intensive color zone by the back surface reflection, and a deep color region where only diffuse scattering is observed. The hair with a porous medulla in Figure 4 also shows the intensive highlight, but an unclear pale color is observed at the back surface reflection and in the diffuse-scattering region. These appearances of the front and back surface reflections and diffuse scattering correspond to the goniophotometric data shown in Figure 3. The apparent color of the poreless hair in Figure 4 looks deeper or darker than that of the hair with a porous medulla. It is interesting to note that the structural difference between the two hair fibers is only the medulla structure. The porous medulla looks like a whitish line at the center of the hair fiber due to the light scattering at the porous structure, as shown in the microscopic view in Figure la and lb. The apparent color, therefore, is different in the macroscopic views of the hairs in Figure 4. The evaluation Poreless Hair Hair with Porous Medulla from surface back surface reflection reflection Figure 4. Photo image of the poreless hair and the hair with porous medulla used in the goniophotometric measurements. Colorless and colored reflections are the front and back surface reflections respectively.

394 JOURNAL OF COSMETIC SCIENCE by the panelists was performed without further color matching, because the apparent color difference is also one of the important influences of internal hair structure on hair appearance in the present study. The apparent color and lightness (especially in the highlight region) perceived in Figure 4 does not directly correspond to the optical goniophotometric data in Figure 2 because the intensity in human perception usually does not linearly correlate to physical inten- sity. In the present study, therefore, the physical data in Figure 2 were converted to the data in the CIE L*a*b* color system as shown in Figure 3. The hair appearance in Figure 4 corresponds to the data in Figure 3. The visual appearances of human hair and artificial nylon hair tresses shown in Figure 5 were compared by professional panelists, in order to clarify the influence of the cuticle structure. The poreless hair of Figure 1 was again used for comparison. The human hair in Figure 5a is the same poreless hair in Figure 4 but taken under different conditions. The members of the panel expressed the view that the human hair was naturally lustrous and colorful, giving an impression of depth along with transparency. On the other hand, the appearance of the artificial nylon fibers was seen to be also intensively lustrous, but metallic and artificial with a flat impression. The human hair with cuticle structure shows clear double reflections: the colorless (more 5a) Human hair tress 5b) Artificial nylon fiber tress Figure 5. Photo images of (a) human hair tress and (b) artificial nylon fiber tress The human hair has a well-ordered cuticle structure and a poreless inner structure. The nylon fiber tress does not have a cuticle structure, but has a flat surface and poreless inner structure.