Speedball Diazo Photo Emulsion is used to prepare a screen for the photo emulsion screen printing method. Basically, you coat the screen and let it dry, lay on an acetate sheet with the image to be "burned", and expose to light. You need ONE OUNCE of Diazo Sensitizer to make 6.6 ounces of Photo Emulsion work! If you make a mistake and need to correct it, or want to re-use a screen for a new image, you will then need Photo Imulsion Remover.