Screen Printing

when you have finished using the screen that you used for the screen, you're "supposed to" to clean it, or can we leave it as it is?

You definitely want to wash after each use. What eventually happens is the paint becomes more difficult to get off once dry, depending on how long you leave it, it can either block the parts of your screen (you do not notice until you start your next printing) or you can muddy other colors or leave it "flakes" in the coming draws. Cold water is recommended because it is less likely to make the emulsion where it is the thinnest on your screen .

Wash your screen is just a good habit to adopt.

Be careful when washing because I had to redo the screen and re-expose when some of the emulsion has been washed.

Yeah, just wash. :]