232 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS In order to test the validity of equation 1, and also to confirm the preceding single-fiber results, a series of tresses was treated with shampoos B 1 and C1 along with four other commercial shampoos and SLS. Table I lists the detergents contained in the shampoos employed, along with any ingredients substantive to hair that they contain. Each of the tresses employed in the current experiments was washed at least five times with a particular shampoo in order to simulate buildup. Following this treatment, hair samples were taken from each tress for light-scattering measurements. Tresses were then mounted on the evaluation frame for assessment by panelists. A large series of shine evaluation panels was run to determine treatment differences among all seven of the shampoos employed. The results are tabulated in Table II, where the rankings are listed in order of decreasing shine. Those treatments connected with a vertical line are not significantly different from each other. Table II also lists the instrumental shine values measured for each treatment, along with the associated standard deviations. The numbers were obtained by calculating an average shine for each tress and then averaging the shine numbers for all tresses treated with the same shampoo. The agreement between the subjective rankings and the instrumental values in Table II was tested using the Spearman rank correlation coefficient method (13). The value calculated for the Spearman rank correlation coefficient was 1.00, which is significant at a level greater than 99%. The agreement between panelists' assessments and instru- mental measurements is thus excellent, and one can conclude, therefore, that the numbers calculated from equation 1 are a reliable measure of hair shine. The results in Table II also indicate that the single-fiber effects reported in the previous section can be expected to be observed under actual usage conditions. Tresses washed with shampoo B 1 were found to be duller than clean tresses, while tresses treated with shampoo B 1 followed by C 1 were found to be duller than those treated with B 1 alone. In general, the shampoo treatments in Table II were found to fall into three main groupings. In the first group, indicated by the first vertical line in Table II, none of the shampoos had ingredients highly substantive to hair. Treatments with these shampoos resulted in the shiniest hair observed, and we consider this hair to be essentially clean. The second group of shampoos in Table II all contained Polyquaternium-10 (a cationic polymer) or fatty acid salts (soap). These ingredients are substantive to hair and can Table I Shampoos Employed in Shine Experiments I Shampoo Primary detergent Substantive ingredients A1 Ammonium lauryl sulfate A2 Sodium laureth sulfate SLS Sodium lauryl sulfate B 1 Trideceth-7 carboxylic acid B2 Sodium laureth sulfate C! Sodium laureth sulfate C2 Sodium lauryl sulfate Polyquaternium- 10 Polyquaternium- 10 Sodium myristate Coconut acid (sodium salts) All shampoos except SLS and A2 were commercial products on sale in the United States. Shampoo A2 was product available in England.

SENSITIVE PROBE OF HAIR SURFACE 233 Table II Subjective and Instrumental Assessments of Shampoo Treatments • Subjective rank 2'3 Instrumental shine 3 Shampoo A1 0.762 (0.10) Shampoo A2 0.714 (0.09) SLS 0.696 (0.03) Shampoo C2 0.602 (0.04) Shampoo B2/shampoo C2 0.582 (0.02) Shampoo B2 0.551 (0.08) Shampoo B! 0.486 (0.03) Shampoo B 1/shampoo C 1 O.427 (O.O3) Assessments were made with a minimum of three tresses per treatment. Treatments are listed in order of decreasing shine. Vertical lines connect treatments that are not statistically different. build up with repeated use. As a result of this particle deposition, the shampoos in group 2 all caused dulling. The third type of treatment effect occurred when the negatively charged fatty acid salts in one shampoo formed a complex with the positively charged Polyquaternium-10 previously deposited on the hair by another shampoo. These types of particles caused the greatest degree of dulling on hair. Although only one example of Polyquaternium-10/ myristic acid dulling is shown in Table II (B l/C1), a second example of this type of interaction and shine loss was observed in single-fiber tests between shampoos B2 and C1. The former product contains Polyquaternium-10 in a sodium laureth sulfate de- tergent system. CONCLUSIONS In this paper, goniophotometric measurements of shine were presented and shown to exhibit excellent correlation with a large series of subjective assessments. In addition to providing a quantitative measure of hair shine, the light-scattering methods presented were also shown to serve as a sensitive probe of the hair surface, permitting one to monitor deposition, removal, and even interaction of particles on hair. Employing the light-scattering methods developed, a group of shampoos containing highly substantive ingredients was shown to dull hair as a result of deposition on the fiber surface, while even worse dulling was observed as a result of interaction on the fiber surface of incompatible particles from different shampoos. It should be noted that the incidence and magnitude of dulling effects from deposition depends on the size of the particles deposited on the hair surface (14). The greatest degree of diffuse scattering and, consequently, the greatest degree of dulling, occurs from particles of the order of 0.4 to 0.7 microns. Particles of the order of 4 microns or larger, on the other hand, will reflect light specularly. Thus, although the substantive ingredients in the shampoos tested in this work caused dulling, it is conceivable that substantive ingredients from other products might be