The photo emulsion is one of the most exciting techniques of screen-printing, offering a wide range of possibilities. This method allows for fine line drawings, various lettering techniques and photographic half tone positives.
A screen prepared with light-sensitive photo emulsion coating A film positive, or printed transparency A light source that will enable you to transfer the opaque positive image to the light-sensitive coating on the prepared screen Note: with the photo emulsion method you should use Speedball’s polyester screens and screen fabric.
1. Mixing the photo emulsion:There are three key things to remember at this step.
Use gloves It is absolutely necessary to add water to the sensitizer and completely dissolve paste the paste into water. Mix with a stirring stick and shake well to help dissolve the sensitizer. You should see a color change in the sensitizer after mixing with water. Thoroughly mix this solution with the emulsion/ The colour will change and the light blue emulsion will now have a green tint. Refer to the Diazo System Process by following the mixing instructions given on both containers. (Always store the sensitized emulsion in a cool and dark place. Shelf life for sensitized emulsion is 4 weeks at 90 F, 8 weeks at 70 F, and 4 months when refridgerated.)
2. Coating the screen
DARK ROOM IS NOT NEEDED FOR THIS STEP. Coat the screen by first adding the emulsion to the screen topside and spread it evenly and thinly across the screen with the squeegee. Use more solution where necessary, spreading evenly with the squeegee. Repeat this process on the backside of the screen, working to achieve an even continuous coating on both sides of the screen fabric. Return any of the excess solution to your mixing container. Do not allow excess solution to build-up, as extra solution will affect proper exposure.
3. Drying of the coated screen
In an area AWAY FROM DIRECT LIGHT AND HEAT, set the screen to dry in a horizontal, bottom side down position. Elevating the four of the under of the frame, allows the screen to dry thoroughly, If more than 300 prints are to be run, it is best to apply a second coating of the sensitized Photo Emulsion to he bottom of the screen after the dirst coat is dry. Remember, for best results aim for a smooth, THIN coating of the solution. Once the coated screen s dry, it must remain in a darkened area until it is ready to be exposed. (Use a fan to greatly speed up the drying of the emulsion on the screen.)
Note that with Speedball’s Diazo System, the maximum allowable time between application of the sensitised emulsion to the screen and exposure of the screen is four weeks at room temperature, in a completely dark environment.