Emulsion is the photosensitive solution that you apply to the screen. It is the key part of screen-printing and is how the image gets “burned” on to the screen, as you will read about in the next step. Applying emulsion needs to be done in a dark room. Make sure there is no light penetrating the room before you open bucket of emulsion.

A bucket of photosensitive screen printing emulsion.

"I use a credit card to apply emulsion," Monaghan said. "Any flexible plastic cards, like a grocery store rewards card, CVS card or student ID will work perfectly fine."

Hold the frame firmly with one hand so it is positioned vertically. Scoop a little of the emulsion out of the container with your card and dab it about an inch away from the edge of the screen. Repeat that until you have a line of emulsion along the top of the screen. Then, pull the emulsion down the screen with the card.

When you reach the bottom of the screen there will be run off emulsion on your card. You can scrape this off into the bucket. The goal of this process is to cover the screen while leaving a one-inch margin from the frame of the screen.

These are two screens are are properly emulsified.

To check and see if your emulsion is applying evenly, hold the screen up the red light in the dark room. The emulsion should look purple. Any places that it is too thick, the color will look darker. Smooth out the dark spots by gently running your card over the area on the screen.

This process is tedious, but it is the most important part of screen-printing. If the emulsion is too thick or too thin, the image will not burn properly onto the screen and you will have to repeat this process again. "You should take the time it takes," said Monaghan. "The thinner the emulsion the better and the more careful you are with your screen the less likely you will have to re-burn it."