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Topic: Fearful of Over-exposing my screen... eek!  (Read 904 times)
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jasfitz
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« on: February 15, 2006 05:47:10 AM »

Hi Guys...

I'm not new to screening at all, actually - i went to art college & used to screen with photoemulsion lots, the only problem being that the school had a lighttable that was set at an 8 minute exposure time.... which means I just have no idea how to judge how long I should expose my images on the lighttable I've just built. I gave it a shot yesterday, at the round old fifteen minute mark, and when i went to the shower to wash the unwanted filler away, it just washed most of the filler away fairly quickly. Definitely sounds like a bad case of the under-exposure blues.

SO... does anyone here know if over-exposing is a bad thing? (for example: If I had left a screen exposing at the 8-minute table at school for, like, 30 minutes.... umm... what would have happened?

OR - do you guys have some clever way of calculating how long I should expose, based on the wattage of light, or something?

I'm thinking I'll expose for 30 minutes this time around... but I'd rather be safe than sorry, and leave it for longer, if I knew it wouldn't ruin things in some way.
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housepig
« Reply #1 on: February 15, 2006 08:39:36 AM »

overexposure (at least with the photoemulsions I've used, Speedball Diazo and Ulano 925) just makes it harder to clean the image out of the screen.

I started with a 30 minute exposure time, and it would take me another 30 minutes of scrubbing and hosing the screen to get the image out. I cut my exposure time to 15 minutes, and it only takes about a minute of hosing down the screen with hot water to make the image pop.

exposure light - a 200w regular bulb in a clamp light 16-18" above the screen.

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jasfitz
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« Reply #2 on: February 15, 2006 08:50:08 AM »

Thanks for the tips Smiley

I think I'm going to stick with the harder-to-clean-out side of things for now.
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housepig
« Reply #3 on: February 15, 2006 11:48:00 AM »

one method I've seen (and would have tried, if I didn't stumble on a good method pretty early) is to make a transparency that has a countdown of numbers on it:

30
27
25
23
...
3
1

prep your emulsion, put this on your screen, and cover everything except 30 with a piece of dark fabric or cardboard. set your timer for 30 minutes. after 3 minutes, pull the cover sheet down to expose "27". continue to do this for every time designation on your transparency.

once you're done, clean out the screen. one of these numbers will come out crisply without being too difficult to clean out; that's your optimum exposure time.

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jasfitz
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« Reply #4 on: February 15, 2006 12:13:26 PM »

SO CLEVER!

I may just have to try that.
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« Reply #5 on: February 16, 2006 04:37:48 PM »

i used a 500 watt flood bulb about 15" away from the screen and it only took about 2 minutes (which is why i overexposed my screens the first few times after exposing for 10 minutes).

so the power of your bulb, the distance you have it away from the screen, and how long you expose will all have an effect on the correct exposure.

i knew some people that were screenprinting for the first time.  they were exposing their screen with a desklamp, so they figured it'd take a while.  they turned the lamp on and went to do something else.  when they came back, it had burned a hole through the screen and shattered the mirror-topped table it was all set up on.

moral: don't leave your screen exposing by itself, and don't expose on top of mirrors.
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