Wednesday, April 29, 2015

Screen printing

Screen printing is one of those fields where instructions are woefully incomplete. You need to screw up a few things to figure out what you're not being told.

Here's the project.

I'd done some screen printing in college, but it turns out there were a few things the teacher did for us that I didn't know about. Which is a problem when you're learning so you can teach others.

Here's a quick summary of how screen printing works. You've got a screen. And you print through it.

More detail? The screen is held taut in a frame. You apply a light sensitive material over the screen and leave it in the dark to dry. You take the design you want on your shirt and print it on a transparency. You know, what your teacher used to use on the overhead projector. Then you put the transparency on the screen and place it all under a bright UV light. The light makes anything not shaded by the ink on the transparency harden. Then you wash off anything that was under the ink. After the screen dries you put in on a shirt where you want it, put colored ink on the screen and put it over the opening with a squeegee. Remove the screen and repeat with as many shirts as you want. Let them dry and use an iron to fix the ink better.

The first thing I didn't know was that the bottle of photosensitive goop isn't automatically photosensitive. You have to add a second bottle and shake it all up. The only thing the instructions said was a single mention of both bottles.

The second thing involved cleaning the screens. Instructions said treat the hardened goop with a chemical and spray it with hot water while scrubbing with a brush. They don't say that the water should be sprayed with a pressure washer.

The third thing was how long to expose the screen to the light. There is a chart that depends on the bulb, the reflector, and a variety of other factors. Exposure can run from only 5 minutes to 45 minutes. 5-8 minutes kinda did the job, but the goop still washed away a bit and pulled away from the screen in places. 45 minutes did the job, but made the girl at the art store look at me in horror. So... 15 minutes next time?
Also, the light says it only lasts 3 hours. So, 1 down. I might need a dark room timer.

Still, I think I've about got one color shirts. Now to try 2 and 3 color shirts.

p.s. - I showed the group 5 colors of shirts. The 4 shown above and one in bright, neon, electric lime. Guess which one they picked.

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