Speedball Screen Printing DIAZO Photo Emulsion is to be mixed with DIAZO Sensitizer #4578 (not included) when doing photo exposure of screen printing screens. The Photo Emulsion method allows for fine line drawings, computer and digital based images, as well as various other images to be screen printed. In addition to the photo emulsion, the sensitizer, film positive of image, and a light source (example: BBA 1 photo flood light) to transfer the opaque images on your positive to the light sensitive screen.