EVALUATION OF LUSTER IN HAIR 483 CORRELATION BETWEEN INSTRUMENTAL AND SUBJECTIVE MEASUREMENT We analyzed the data to determine if results from the instrumental analysis and the panelists' subjective assessment were in agreement. A comparison of the instrumental results with the results from the panel test indicates that luster value from SAMBA was inversely proportional to visual luster ranking assessed by the panelists (Figure 6). Collectively, the scores from the panel test were in good agreement with the luster measurements obtained from SAMBA. The panelists' assessments demonstrate that consumers' perception of hair shine depends not only on the increase in specular reflec­ tion but also on the reduction of width of the reflected light. This reduction of width was caused by a narrowing of the shine band, so that panelists easily felt much more spotlight above 1 % phenyl trimethicone treatment than below 0.5%, and it was clearly visible for panelists at 2% phenyl trimethicone treatment. DISCUSSION We used a polarimetric camera with a high polarization contrast parameter value at a fast video rate (30 frames/sec) to quantitate shine using polarized illumination. SAMBA provided reliable results for luster measurement and a rapid, easy, and quantitative means of determining the shine effect of silicone on hair tresses. 40 r2 0.84 30 • ,-. � 20 fl.I ·-� a.. 10 � fl.I 0 -10 -------------------.---------------, 10 20 30 40 50 60 70 80 Total luster ranking Figure 6. The correlation between luster increase(%) as measured by SAMBA and subjective luster ranking by panelists.

484 JOURNAL OF COSMETIC SCIENCE In order to reduce the tremendous variation when tresses are positioned on the cylinder due to hair fiber variability, it is essential that the alignment is always the same whenever the measurement is carried out, particularly when comparing silicones that have similar shine effects. Because this variation can cause a bigger difference in the shine measurement than results from the application of different silicones to oriental hair tresses, we modified the procedure to avoid the variation by repositioning the hair tress between SAMBA measurements. Our experiments showed that we could achieve con­ sistent results using SAMBA by applying the silicone to the positioned hair tress and measuring the same area of hair before and after treatment. We chose to treat the hair tresses with phenyl trimethicone, which is ethanol-soluble and non-volatile. Phenyl trimethicone is commonly used in leave-in cosmetic formulations as a shining agent and has the ability to coat the hair surface (1,10). All concentrations of phenyl trimethicone increased the luster of hair tresses. We found that the luster increase of oriental hair tresses upon treatment with silicone depended on specular reflectance (S) and the peak width at half-specular reflectance (W 112 ). The change in diffuse reflectance (D) was relatively low, due to the dark-brown color. AFM is a powerful method used to perform tribological measurements. The application of AFM to the study of hair has made it possible to image film formation on hair fibers on a nanometer scale and to study the nano-effects of hair care products. With AFM data, we were able to identify that the increase in luster measured by SAMBA was caused by a reduction in roughness. Because the effect of luster is greatly affected by the surface condition of the hair fiber, silicone film formation on hair fibers makes the hair smooth, increasing the intensity of specular reflection and decreasing the diffuse reflection in­ tensity. We measured the same area of untreated and treated hair fibers with AFM to obtain objective results and to eliminate individual hair fiber variation. We measured the same area of untreated and treated hair fibers with AFM and found that film formation and reduction of roughness could be consistently measured following treat­ ment (Figure 4, Table I). We conducted a panel test with 15 untrained panelists to obtain their subjective assessments of hair luster in phenyl trimethicone-treated tresses. Panelists easily recog­ nized the luster difference between untreated and treated tresses, but had trouble dis­ tinguishing the shine between tresses treated with 0.1 % and 0.5% phenyl trimethicone. However, they were able to distinguish the shine between tresses treated with below 0.5% and those treated with over 1 % phenyl trimethicone. The results from the pan­ elists were in good agreement with the luster increase obtained from instrumental measurements. Thus, using our modified protocol, SAMBA measurements were effective in comparing the luster values of silicone-based compounds. CONCLUSIONS We found that SAMBA provides reliable results for luster evaluation and a rapid, easy quantitative means of determining the shine effect on hair tresses. AFM studies provided convincing evidence that phenyl trimethicone increases the luster of hair fibers by film formation on the hair surface. These results show that SAMBA has utility as an instru­ mental technique for hair luster evaluation and is in good agreement with consumers' subjective evaluation of luster.