226 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Dye treatments consisted of placement of a swatch in 40 ml of a 0.5% solution of dye for 30 seconds. The swatches were then rinsed under 100øF running tap water for 30 seconds and hung up to dry. MEASUREMENT OF SHINE Shine, or luster, is perceived when an object scatters much more light at a particular angle or in a particular direction than in other directions. Under these conditions, surface highlights or brightness contrasts appear and the object is seen to be shiny (see, for example, references 6-8). In order to measure shine, therefore, one needs to be able to measure scattered light intensity as a function of angle. This is accomplished with a goniophotometer. Figure 3 shows, in rudimentary fashion, the operation of such an instrument with a hair fiber sample. In this case, the fiber is assumed to be held taut and is irradiated with light at an incident angle, i, that is prechosen and is measured with respect to the perpendicular to the fiber. The intensity of that portion of the incident light that is scattered by the hair is measured by rotating a photomultiplier tube, or light detector, from 0 ø to 75 ø. The illustration shows two of the positions of the photomultiplier tube. Typical results from a goniophotometer measurement are shown in Figure 2 for an undamaged Oriental hair. The light-scattering scan is presented as a plot of scattered light intensity as a function of angle. Figure 3. Rudimentary diagram of a goniophotometer experiment. A hair fiber is held taut and struck by incident light at angle i. Scattered light is then detected by rotatin'g a photomultiplier tube from 0 to 90 degrees with respect to the perpendicular to the fiber. Two of the photomultiplier positions are shown.

SENSITIVE PROBE OF HAIR SURFACE 227 The incident light in this experiment was set at 30 ø, and one can see a maximum in the measured curve near this angle. This is termed specular reflection. Light is also scattered at angles other than the specular this is termed diffuse reflection. This latter type of scattering is caused by light hitting the scale edges of the hair. It can also be caused by small imperfections on the hair surface and, in addition, by deposited particles. An excellent discussion of the morphological features of hair that give rise to observed light-scattering patterns can be found in reference 1. The question now arises as to how one can use the goniophotometric results to measure shine or luster. From the definition of shine, it appears obvious that luster increases with increasing specular reflection and decreases with increased diffuse scattering. Any func- tions used to estimate shine must therefore take these two relationships into account. Several workers have developed shine functions, employing these relationships for ap- plications such as textile fibers, polymer surfaces, etc. [see, for example, (2,6-10)]. In this work, several functions were tested both from the literature and also devised by ourselves. The best agreement with subjective evaluations was found using the rela- tionship L = S/DW(V2) (Eq. 1) where L equals luster or shine. D in this expression is the integrated diffuse reflectance and is obtained, as in reference 2, by connecting the scattered light intensities at 0 ø and 75 ø and measuring the area under the resulting line. S in equation 1 is the integrated specular reflectance and is obtained by measuring the area of the specular peak, while W(Vp) is the width of the specular peak at half-height. All three of these quantities are illustrated in Figure 2. It has been pointed out (2) that use of expressions such as equation 1 with D in the denominator are valueless for cases where diffuse reflectance goes to zero. For most cases involving hair, however, scattering off the scale edges insures a minimum value for D, so that equation 1 is broadly applicable. In the current experiments, hair fibers from treated tresses were scanned one at a time in the goniophotometer. There is tremendous variation from hair to hair, even from a single head of hair, so that in order to obtain meaningful shine values for a particular treatment, an average of many hairs must be taken. In the current case, 21 hairs were taken from each tress, while three tresses were employed for each treatment. Each shine value, therefore, represents an average taken from 63 hairs. RESULTS AND DISCUSSION SINGLE-FIBER SCREENING TESTS Figures 4-6 show typical light-scattering scans taken after a series of shampoo treat- ments of single hair fibers. These types of single-fiber experiments are useful as a means of rapidly screening the effects of various treatments on hair. The results from these experiments can only be treated qualitatively, however, since they represent treatments on single hairs and there is too much variation among hairs for