OPTICAL DISCRIMINATION OF SKIN 12 5 Figure I. Color photography of the hand: A) Using conventional flash illumination. B) Using polarized flash illumination and a polaroid filter on the camera lens oriented parallel to the incident light. C) As (B) but with the polaroid filter turned through 90 ø and crossed with respect to the incident light. the orientation of the polaroid filter on the camera is changed to perpendicular with respect to those on the lamps, give a record of those areas where depolarization has occurred. It is clear that the distribution of red in the skin does not have any obvious superimposed contribution from surface reflected light. Not only has the sheen gone but also the bulk of the fine detail from the stratum corneum. These differences are more obvious if the photographs are scrutinized with a x 3 to x 5 magnifying lens. The surface sulci are more clearly delineated in Figure lB than in Figure 1A. Figure 1C, however, shows clearer delineation of underlying redness than Figure 1A. A mottled pattern is obvious in the depolarized image which is not at all clear in the unpolarized image. Major folds in the palmar surface and that of the fingers, where the stratum corneum is thinner, are clearly outlined in red with greater contrast than in Figure 1A. Under magnified examination a subtle network of fine white lines

126 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure lB can be seen within the skin folds over the joints of the fingers. These same areas have the appearance of dryness in Figure 1A and must originate from regions of surface scatter and depolarization of reflected light. A similar effect can be found on the palmar surface near to the base of the fingers and the hypothenar eminence. The reference metallic surface in each photograph demonstrates clearly the near extinc- tion of the polarized light with a crossed polaroid filter. Depolarized light from the reference white standard shows little change with the orientation of the polaroid filter on the camera, and therefore any observed changes in detail or color must originate from preferential interaction with the skin. POLARIZED REFLECTION SPECTROSCOPY OF HUMAN SKIN Figure 2 shows the reflection spectra from the hypothenar eminence of the hand ob- tained using an integrating sphere with the Perkin-Elmer Lambda 7 spectrophotom-