Abstract: A transmissive system for characterizing the photochemical reactivity and solubility properties of materials, such as photoresist, that contain one or more photo-active constituents and that can be formed as films on optically-transparent substrates. The system operates to detect the intensity of light transmitted through the photo-active material and the optically-transparent substrate. Generally speaking, the system comprises: a) an optically-transparent substrate means for providing a substrate for a film formed of a material that contains one or more photo-active constituents; b) exposure means for transmitting at least one selected wavelength of light through at least one selected area of the film; and c) detection means for detecting the intensity of light transmitted through the film and optically-transparent substrate means.