AUTOMATED DEVICE TO ASSESS HAIR SHINE 461 assessment as the standard of reference, the accuracy of the opsira Shine-Box assessment is 75%. Thus, there is a good agreement between both methods. Effect of hair color on the objective shine value. To assess the need for stratifi cation on hair color, basal objective hair shine values were determined using hair tresses of different ethnic origin and color. As shown in Figure 7, both components of objective hair shine— specular and diffuse refl ection—behave differently depending on the ethnic origin and color of the hair tress investigated. As a general rule, the blonder the hair the better inci- dent light is refl ected, resulting in a higher specular component of refl ection (Figure 7A). In the same way, blond hair absorbs less light inside the hair, also resulting in higher dif- fuse refl ection as compared with dark hair (Figure 7B). When calculating the objective shine value or luster (L) using the equation of Reich/Robbins (eq. 1), the high specular refl ection of blonde hair is more than compensated by the corresponding diffuse refl ec- tion, resulting in generally higher objective shine values of dark hair (Figure 7C). Strati- fi cation of hair color is therefore a prerequisite to obtain comparable objective shine values in a series of measurements. Objective shine values are generally higher when using dark hair. In addition to this, the dynamic range achieved by the application of a shampoo is much better with brown hair. As shown in Figure 8, substantial additional effects of shampoos on objective hair shine are seen with brown hair. In contrast, a smaller dynamic range in terms of hair shine is seen with the same hair care products on blond hair. As a consequence, stratifi cation of Figure 7. Basal objective hair shine values of hair tresses of different ethnic origin and color. (A,B) Specular and diffuse integral refl ection values of hair tresses of different ethnic origin and color. (C) Calculated objec- tive shine values (luster) using the equation of Reich/Robbins.

JOURNAL OF COSMETIC SCIENCE 462 hair color is indispensable for automated assessment of hair care products regarding their effects on hair shine. Brown hair tresses or other tresses that have not been aggressively bleached are the test material of choice in this regard. Effect of combing on the objective shine value. To assess the effect of parallelism (combing) of hair tresses on the determination of objective shine values using the opsira Shine-Box, the same tresses were mounted on the carrier with different degrees of parallelism. A com- parison of recorded shine values and the corresponding combing values shows that the higher the objective shine value the better the parallelism of the analyzed hair tress (data not shown). As a consequence, to assure comparability of results between hair care prod- ucts, hair tresses have to be excluded from analysis when a suffi cient degree of parallelism is not given. In such cases the hair tress has to be recombed until suffi cient parallelism is gained. Reproducibility and sensitivity of objective shine values. Provided a tress is well combed, re- peated measurement of shine values at a defi ned position on a hair tress results in variances of only 0.3–1%. In contrast, measurement at different positions on a well-combed tress may result in in variances of up to 5%, and with leave-in products that cannot be distrib- uted homogeneously over the hair tress, the respective variability may be up to 8% (data not shown). As a consequence, to increase the robustness of measurement, the objective shine value of a hair tress is determined by averaging shine values determined at three or four different positions on a given hair tress. The variability of this averaged objective shine value is approximately 1% in repeated measurements, even if different positions on the hair tress are evaluated in repeat measurements. Figure 8. Dynamic range of the change in objective hair shine values of brown (A) and blond (B) hair tresses treated with different hair care products. Brown hair tresses provide a suffi cient dynamic range to as- sess shine-promoting properties of hair care products.