OK, so you have wasted hours of work and expensive emulsion trying to burn a screen and still you end up with a crap screen that won’t wash out or is a slimy mess that all washes out. So, then you ask how long do I expose my screens for? This is the question most new people ask when getting into screen printing. The answer is a firm, that depends.
It depends on the brand and type of emulsion, number of coats of emulsion on the screen, time of day, moon cycle and a host of other factors. The best way to find out the best exposure time is to use a test strip or exposure tool. Exposure tools are printed on a clear plastic and have different gradients from light to dark.
These strips can cost upwards of $30 bucks but, there is a cheaper way. Take a piece of art work that you have printed out on acetate and cover a portion of it with construction paper. Expose the screen for one minute. Then you move the construction paper to expose the next portion of the art image and expose again for another minute.
Do this 5 times and you will end up with a screen with 5 different exposure times on it from one minute to five minutes. Wash out the screen and the area that washes out the best is your exposure time. Anytime you are having problems with exposure, do this test and recalculate your times. You will definitely want to do this when you change emulsion type / manufacture or go to another mesh count screen etc.
So start using test strips today get great screens that make screen printing easy and fun