MEDULLA STRUCTURE AND HAIR APPEARANCE 97 2O 15 - 10 0-20 20-40 40-60 60-80 80-100 Score of porous medulla Figure 10. Distribution of panelists ranked by the amount of medulla accompanied by light scattering. Panelists of Figure 9 were classified by the way a hair dryer is used. Open column: non-user of a heat dryer. Gray column: panelists finish to dry before full dry state. Closed column: panelits finish to dry after full dry state. (a) 60øC (b) 80øC (c) 120øC I /hm !mm mm (d) Before heating (e) After heating 3 •tm 3 •tm Figure 1 I. Upper: Optical microscopic views of fibers after heating with a dryer for five minutes at 60øC, 80øC, and 120øC (from left to right). Lower: SEM microphotographs of the medulla in a hair cross section before and after heating for five minutes at 120øC.

98 JOURNAL OF COSMETIC SCIENCE 100 80 60 40 20 0 '[__ ! [•j •"1 80 Temper •:v 70 oc 5 4 3 2 1 0 60 of hair / Cycle times of heating / times Figure 12. Increase of porous medulla as function of both numbers of cycle times of heating and heating temperature. and the low-angle region (around 10 degrees), while the contrast is higher in the case with fewer medulla pores to show a distinct peak around 55 degrees. This peak in the chroma curve leads to a brilliant impression. Futhermore, the hue angle of hair with fewer medulla pores shows variation according to the receiving angle (Figure 8c), but it is almost constant with more medulla pores. These results mean that apparent hair color with less porous medulla is highly dependent on the viewing angle, while the color with more medulla pores is relatively independent on the angle and is monotonous From the above results, it is understood that the appearance of hair with more porous medulla is lusterless and dull because of low contrasts of lightness and monotonous apparent color, while the appearance of hair with less porous medulla is shiny and brilliant because of that high contrast. PORE GENERATION AT THE MEDULLA BY DAILY HAIR CARE PROCESSES Figure 9 shows a distribution histogram of panelists where the abscissa denotes the scores of the total amount of light scattering from the medulla. The scores of scattering light must roughly correspond to the lengthwise ratio of the total whitish portion against the total fibers in microscopic views. It should be noted that the score does not strictly correspond to the amount of porous medulla, because it is sometimes difficult to evaluate scattering at the fiber center in the case of considerably dark hair, even by using an intense light source. It can be said that, more or less, 80% of the panelists have porous medulla. Through this survey, it was also noticed that the amount of light scattering from the medulla in the panelists may have some relationship with the hair care behaviors of the individual panelists. Figure 10 shows the histogram of the same panelists as those in