Screen coating is one of the trickier aspects of the print making process. It requires a bit of practice and a good deal of control and co-ordination.
First off, it is important to start with a clean screen. Even if you are using a new screen, you should degrease the mesh before coating.
There are commercial degreasers available from screen suppliers, but a simple solution of washing detergent and water will do the job. Just fill up an empty spray bottle.
DEGREASING
Spray the solution onto the screen, then use a clean scrubbing brush (not a heavy duty brush, just a nail brush with bristles that aren’t too coarse) to push the solution around the screen. You should work up a bit of a lather like this. Scrub both sides of the mesh. This process is intended to get rid of any impurities and/or residue from other products or anything that could repel the emulsion and stop it from adhering to the mesh. The entire screen should be thoroughly rinsed out and dried.
The use of the scrubbing brush also helps prepare the mesh to take the emulsion, giving it a slightly rougher surface for the coating to hold onto.
When your screen is drying, both after degreasing and coating it needs to be protected from any dust or dirt, and after coating, it is imperative that it be protected from light, as the emulsion is light sensitive and premature exposure will render your screen useless. A box big enough to house the screen is ideal. Most screen printers have drying cupboards with racks so the screens can be dried horizontally for an even coating.
When your screen has been degreased and dried, it is ready to be coated. For this we use a scoop coater, or screen applicator.
COATING WITH PHOTOGRAPHIC EMULSION
1. Be sure to give your emulsion a good gentle stir before pouring it into your applicator. Make sue your applicator is clean. Carefully pour some emulsion into the applicator. Make sure you do this and the following steps in subdued lighting.
2. Place your screen vertically on a sturdy bench. Hold it at the top so that it can be tilted back and forth while you are coating. (If you are right handed, hold the screen with your left hand and vice versa for lefties.) Hold the applicator to the bottom of the mesh, manouvre it so the emulsion lines up evenly across the width of the screen.
3. Tilt the applicator up so the emulsion makes contact with the mesh. Draw the applicator slowly up the screen, while maintaining strong contact with the mesh. When you reach the top of the mesh, stop. Tilt the applicator down to allow excess emulsion to run back into the applicator, then scrape up as you pull away so it doesn’t drip.
4. Turn the screen around and repeat the step. When you coat the other side, excess emulsion will be pushed back through the mesh to the opposite side. Every screen printer has different ways of doing things. Some will leave it at that, some will scrape one or both sides of the screen to remove the excess. Some will only coat one side. It is a matter of experimenting with what works best for you.
If you make a mistake, just scrape both sides and start again. When you are done, retain any excess emulsion for future use.
This is a good demo video.
http://youtube.com/watch?v=FxIuiff1TNs
