812 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS INTEGRATING SPHERE EPIDERMIS AND SUNSCREEN AGENT ,( LIGHT SOURCE PROPOSED METHOD PHOTOGRAPHIC PLATE '• '( LIGHT SOURCE ,( OLD METHOD Figure 3. Proposed modification of photographic method over a group of cells (Fig. 3). Such a registering device more accurately would account for the scattering potential of sunscreens, as shown by Master et al. (3). PHOTOGRAPHIC METHOD Materials and Methods The apparatus consists of a lensless Compur shutter set at 1/250 see with an aperture of f 7.7. This is placed over a sliding piece of card- board which covers four cylindrical ports (Figs. 4 and 5). A foam rubber gasket on the underside of the shutter assembly eliminates ambient light when the shutter is firmly compressed. A sliding cardboard assembly with a filter attachment is placed over the cylindrical openings. An optical glass filter, UG 11 (Schott), allows only ultraviolet light of wave- length less than 4000 • to pass to the plate. The filter is moved from one port to the next after each exposure. The four cylindrical ports are so constructed as to fit against the slide plate without scratching it and at the same time protect the film from ambient light. The sliding port mechanism is housed over a View camera back. Within the camera back, 4 in. X 5 in. Kodak projection plates are held and covered by a plate holder. An important irregularity which might result from un- equal spectral sensitivity of film is avoided by always using Kodak medium contrast projection slides, which are equally sensitive to all the ultraviolet wavelengths tested by this system (Fig. 6) (4). This was confirmed by testing with monochromatic light.* * H. T. Hudson, R. G. Freeman, Baylor University.

Figure 4. SUNSCREEN TESTING METHODS Ero•t bfshutter :and sponge Sliding po•f. cover a.d :filter :. :: . : . ::-. ....... Ca• •'.hack :•"d plat e h01der ß op •ie• o[ sep•mte• c•em •ssemb]y use• [o[ testing su•sc[eem eompo•e•t •s d•gmmmed (fight) •d photographed (]e•t) •o[ cidCry 813 Each cani'e'r a :bQCk •n d plat e, holder 'Ports ii: 'Back: :of shutter and •pouge:: :..':::7.7'• ......... . .... Figure 5. Bottom view of camera assembly ::Ports