Speedball Diazo Sensitizer is an important ingredient of the photo emulsion process. The photo emulsion method of screen printing is perhaps the most exciting method created. It makes fine line drawings, computer generated images, various hand and commerical lettering and photographic half-tone positives. The photo emulsion method requires a screen prepared with the photo emulsion/sensitizer mixture, a film positive or a printed transparency film, and a light source that will transfer the opaque images on your positive to the light sensitive printing screen. DIAZO Sensitizer must be mixed with Diazo photo emulsion. Sensitizer bottle appears empty, but actually contains condensed paste that is to be 3/4 filled with water.