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J. Cosmet. Sci., 51,289-302 (September/October 2000) Measurement of hair luster by diffuse reflectance spectrophotometry CARLA SCANAVEZ, MARCO ZOEGA, ANDR]•IA BARBOSA, and IN]•S JOEKES, Instituto de Qu/mica, Universida& Estadual de Campinas, UNICAMP, Caixa Postal 6154, CEP 13083-970, Campinas-SP, Brazil. Accepted for publication August 31, 2000. Synopsis We studied the application of the diffuse reflectance spectrophotometry technique in order to obtain consistent hair-luster measurements. The influence on data quality of such experimental conditions as sample color, texture, geometry, and position, and of such instrumental operating conditions as viewing angle, viewing aperture, and inclusion or exclusion of the specular component, were established. The color- difference parameter (DE) appears as the best parameter to measure hair luster in CIELAB and FMCII systems of equations. Hair tresses submitted to several treatments, including shampooing and conditioning, were used to choose the best reference (zero-luster value) and hair-luster saturation (maximum-luster value). A luster scale was assembled from DE values, pointing out that diffuse reflectance spectrophotometry data allows measuring and quantifying hair luster. INTRODUCTION Luster is an essential quality for hair beauty. However, it is difficult to measure it by physical methods. The literature describes a few light-scattering measurements using goniophotometry (1-5), but usually visual evaluations are applied for describing hair luster. In fact, luster or gloss is an optical phenomenon that results from the specular reflection of light (referring to the mirrorlike reflection) from a smooth surface. As the surface becomes rougher, the luster is reduced and the diffuse reflection from the surface increases. A completely nonlustrous rough surface is a diffuse reflector (6,7). Therefore, diffuse reflectance spectrophotometry should be able to measure luster. This is a well known method for color measurements in opaque substances and surfaces, widely ap- plied in the paint and paper industry (6) however, it has not been applied to luster measurements. We have investigated the capacity of simple diffuse reflectance equipment to measure hair luster. From the spectra, an ordinary software calculated color parameters as defined by two color systems, CIELAB (Commission International on Illumination L*, a*, b*) and FMCII (Friele-MacAdam-Chickering), both based on just-perceptible differences of color. Lightness difference (DL), chromaticity difference (DC), and color difference 289