LIGHT SCATTERING THEORY TO MEASURE RINSABILITY OF HAIR CONDITIONERS 403 modeled as indicated by the second bar in the fi gures. For time constant, the higher the value of the bar, the faster the conditioner rinses off. For the residual material, the higher the value of the bar, the more residual material left on the hair after rinsing relative to the time constant. As seen in Figure 4, Conditioners A and D exhibit comparable time constant values on bleached hair, as indicated by the steepness of their slope. Yet, relative to their residual bar, Conditioner A has a much higher residual value compared with Conditioner D, indicating that although both conditioners rinse out quickly, Conditioner A has much more condi- tioner material remaining on the hair because of its substantivity. Conditioner C displays the smallest time constant value, demonstrating that Conditioner C had the longest rinse out time. Its residual component with respect to its time constant indicates that Condi- tioner C has a high amount of residual material left behind. Thus, although Conditioner C took the longest time to rinse out compared with the other systems, it still has a con- siderable amount of material left on the hair surface. Similar analysis can be performed on virgin hair. As depicted in Figure 5, Conditioner D, the negative control, has the highest value for the time constant and the lowest residual value relative to the time constant, indicative of a product that rinses out faster, leaving very little material on the hair compared with the other conditioner systems. Condition- ers A and B have similar values time constant and residual values, indicating that these materials have similar rinsing performance on virgin hair. Conditioner C has the smallest value for the time constant, indicating it took the longest to rinse out. Its residual com- ponent with respect to its time constant indicates it still has a high amount of residual material left on the hair relative to the other conditioner systems. Figure 6. Combing performance, average total work, of four conditioner systems on European bleached hair.

JOURNAL OF COSMETIC SCIENCE 404 COMBING PERFORMANCE Once the rinsability profi le of the different conditioner systems had been established, it was important to compare against their conditioning/combing performance. Figures 6 and 7 depict the absolute values of the average combing force of the treated and rinsed bleached and virgin hair tresses as related to the average total work performed for the four condi- tioner systems tested in the rinsability study. Notice in both fi gures, Conditioner D has the highest combing force, indicating poor conditioning performance compared with the other conditioners. This correlates well to the rinsing data seen previously as Conditioner D is our negative control non-ionic system, and it is expected to not condition the hair as it’s not substantive and thus won’t deposit, and thus will rinse out the quickest. However, notice that Conditioners A, B, and C virtually exhibit comparable combing performance on both bleached and virgin hair. No statistical difference in combing force is seen among these three conditioner systems, but yet there are signifi cant differences in their rinsing behaviors which can be attributed to their chemistry, confi rming the introductory statement that study- ing hair surface attributes alone such as combing and friction is not suffi cient to understand how a product behaves in terms of rinsability. This new rinsability test method confi rms that subtle differences can be distinguished in the rinsing profi le of different product chemistries. CONCLUSION A quick and simple optical method has been established and applied to quantitatively mea- sure the rinsability of conditioner systems on different hair types. Using the Beer–Lambert relationship, non-absorbing particles can be measured with light scattering techniques to Figure 7. Combing performance, average total work, of four conditioner systems on European virgin hair.