JOURNAL OF COSMETIC SCIENCE 324 The effects of the contrasts are, on the other hand, not obvious in blonde hair’s appearance. Instead, a former study by the present authors regarding blonde hair’s appearances showed that blonde hair panelists are inclined to prefer brighter appearance with less contrast in brightness and color and that the softly toned color is indispensable in order for blonde hair to look blonde (16). The origin of the word “blonde” is old Germanic, meaning the particular kind of color, “yellow/yellowish-brown” or “light colored,” and the word is used only for hair color. The color is, however, not the only attribute to describe blonde hair’s appearance. As many examples are easily found in lines of poems and in expressions of drawings, blonde hair’s appearance has also long been associated with light, rays of light, and strong shine. In fact, it is often experienced that blonde hair shining brightly is accompanied by a soft tonal color when it is observed under the sun or a strong light source. We studied the optical mechanisms of the bright shine of blonde hair that is closely related to its beauty. EXPERIMENTAL Chemically untreated Caucasian blonde hair (Most Bright) from De Meo Brothers Inc. was used. Hair fi ber diameters were measured at 20 points for each fi ber at 1-mm inter- vals along a fi ber axis with a laser optical measurement system, a diameter measurement device (SK2000, Kato Tec. Co., Ltd.). In order to understand light refl ection behaviors, refl ection intensities of a fi ber were mea- sured with a goniophotometer (GP-200, Murakami Color Research Laboratory Co., Ltd.). In this system, the parallel incident white light beams reach the specimen surface through the beam iris. The beams refl ected or transmitted from the specimen plane are fed to the receptor. Thus, the refl ectance, transmittance, and diffuse refl ectance of the specimen can be obtained by measuring the light intensity. The defi nition of incident angle and receiv- ing angle in the measurements is illustrated in Figure 2. Goniophotometric measure- ments were carried out with two different arrangements of a sample fi ber. In the normal arrangement (Figure 2a), measurements were performed under the condition that the irradiation light angle of incident light was fi xed at a right angle to the fi ber axis (0°), and the detector was operated in the plane perpendicular to the fi ber axis, including the irradiation light source. In the coplanar arrangement (Figure 2b), measurements were performed under the conventional optical measurement conditions, i.e., incident light Figure 1. Structure parameters and optical events.

MECHANISM FOR HAIR SHINE 325 was irradiated in a coplanar manner to the hair fi ber (-45°) and the detector was moved in the coplanar plane from 0° to 90°. RESULTS When a blonde hair fi ber is observed by the naked eye, irradiated under directional light with a dark background, the appearance of the blonde hair fi ber varies drastically by po- sitional relationship with the light source, the sample, and the viewpoint. For example, the shiny appearance of a blonde hair fi ber greatly changes depending on whether a fi ber axis is coplanar with the light source and the viewpoint (the irradiation-observation plane) (Figure 2b) or vertical to the irradiation-observation plane (Figure 2a). While fi bers appear to be similar in their shine to each other under the coplanar conditions, each fi ber was found to look quite different, i.e., some shine very brightly but others do not under the normal conditions. The fi bers with intense shine (Group A) and the fi bers with less shine (Group B) were judged under the normal arrangement conditions and set apart from one another. Figures 3a and 3b show photographs of the fi bers mounted on a black board obtained according to the positional relationships shown in Figures 2a and 2b, respectively. The two different types of appearance were confi rmed to exist generally in blonde panelists. The averaged diameters and ellipticities (E = minor axis/major axis) of these hair fi bers in Groups A and B are shown in Table I. For all hairs in both Groups A and B tested, the refl ection peak from the front surface of the fi ber was observed at around the receiving angle of θ = 40°, and that from the back surface was at around θ = 50° to 60° in the coplanar arrangement. Typical examples of the refl ection intensity curves are demonstrated in Figure 4. The difference between the maximum peak intensities and the average integral intensities of the refl ections of these two groups (Table I) were not big enough to explain the apparent differences in Figure 3. Figure 5 demonstrates one of the typical examples of the refl ection intensity curve ob- tained in the normal arrangement measurement. As in Figure 5a, the peak intensity of a Figure 2. Defi nition of optical arrangements in goniophotometry: (a) the normal arrangement (b) the co- planar arrangement.