Support material 12 can comprise any of a variety of transparent plastic sheet materials such as the cellulose esters (e.g., nitrocellulose, cellulose acetate or cellulose acetate butyrate), polyesters, polycarbonates, vinylic plastics such as the acrylics or vinyl chloride-acetate copolymers, or other plastic materials that can be provide in a sheet-like, light-transmissive form.