THERMAL TREATMENTS WITH A CURLING IRON 27 linkages and hydrophobic bonding, leading to significant increases in fatigue resistance (increases in characteristic life). The outcome of this study suggests that curling of hair under moderate conditions specified by the manufacturer of the curling iron is not damaging to hair. On the contrary, it may be beneficial when used in combination with certain conditioning polymers. ACKNOWLEDGMENTS This research was carried out in context with our "Characterization and Quantification of Hair Damage" project, which is supported by TRI corporate participants from the international hair care industry. We thank TRI staffers Amy Lyttle for the tensile mechanical testing and Elena Petrovicova for the fatigue measurements. REFERENCES (1) W. Weibull, A statistical distribution function of wide applicability,]. Appl. Mech., 18,293 (1951). (2) M. Hara, P. Jar, and J. A. Sauer, Fatigue behavior of ionomers: Effect of concentration on sulfonated polystyrene ionomers, Macromolecules, 23, 4465 (1990). (3) M. Gamez-Garcia, The cracking of human hair cuticles by cyclical thermal stresses,]. Cosnzet. Sci., 49, 141 (1998). (4) S. B. Ruetsch, Y. K. Karnath, and H.-D. Weigmann, The role of cationic conditioning compounds in reinforcement of the cuticula,J. Cosnzet. Sci., 54, 63-83 (2003).

]. Cosmet. Sci., 55, 29-47 Qanuary/February 2004) Optical properties of hair-Detailed examination of specular reflection patterns in various hair types R. McMULLEN and J. JACHOWICZ, International Specialty Products, International Specialty Products, Wayne, NJ. Accepted for publication September 11, 2003. Synopsis Details of the specular reflection of curved hair tresses, resulting from illumination with a collimated incident light source, were examined both qualitatively and quantitatively using high-resolution photog­ raphy and image analysis. The reflections were found to consist of a multitude of light dots aligned with the fibers and typically separated by a distance of 81-145 µm. The contrast between the dots (specular reflection) and the darker regions (diffuse reflection) of the entire reflection band was found to increase with increasing pigmentation of hair. Highly pigmented Oriental hair provided more contrast within the specular reflection band than unpigmented natural white hair. A quantitative description of the light reflection patterns within the specular reflection band included two-dimensional distribution of luminosity, histograms of the frequency of appearance for peak maxima and minima in luminosity distribution plots, and histograms of absolute maxima and minima of luminosity along the length of the fibers. Specular reflection from African hair, which consists of many curls that provide multiple and randomly distributed reflection centers, have also been investigated. Using microscopy software, Image Tool 2.0, and a method termed image threshold, the number of reflection sites and their shapes could be quantified. For example, treatment of African hair with synthetic sebum was shown to significantly affect the reflection patterns, resulting in a decrease in the overall hair luster. Comparison of reflection patterns from Caucasian frizzy, very curly, and curly hair is also discussed. INTRODUCTION In a previous report (1), we described the measurements of luster for various types of hair by quantifying the intensity of light reflected from hair fibers spread over a cylindrical surface and illuminated by a collimated beam of light. Such an experimental setup allows one to obtain reflected light distribution curves similar to those typically generated by goniophotometers. By analyzing the shape of the reflection curves and by calculating luster parameters, we were able to investigate the effect of polymer and oil treatments on the luster of hair. While performing this analysis, we took note that the specular reflection band appeared to consist of a series of discrete microreflections arising from individual fibers and corresponding to the structural elements located along the fiber length. Thus, the specular reflection is not a continuous and uniform plane of light but possesses a dot-like or striped appearance. It should be emphasized that this effect is not only detectable by using high-resolution photography but can be easily observed with 29