Author Topic: How to under expose a screen?  (Read 1787 times)

Offline Gilligan

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How to under expose a screen?
« on: January 15, 2013, 01:59:44 AM »
Almost a serious question.

Older MSP 3140 with a new bulb (not that it matters really).

We did a new step wedge test (desperately needed), we took a chromaline blue coated fairly thick, if memory serves me 50% EOM, on 150-S yellow mesh.  We started at 15 light units and went 4 units up each time for 10 test.

Started developing it and couldn't hardly get blue to come off on a paper towel rubbing it back and forth with some pressure.  ZERO slime.

It was technically under exposed in my opinion until step 4 or 5 (27-31 Light Units) as it didn't hold well below and wasn't washing out as well above.  This is developing with COLD water (40 degrees outside) and a cheap pressure washer (it's on the list).

So, I don't really have a real question but does this seem right?  Shouldn't I have gotten some slime on there?


Offline alan802

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Re: How to under expose a screen?
« Reply #1 on: January 15, 2013, 09:29:24 AM »
shirt side or squeegee side?  Should have had some definite slime on the squeegee side, maybe not the shirt side.
I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it -T.J.
Those who expect to reap the blessings of freedom, must, like men, undergo the fatigues of supporting it -T.P.

Offline Gilligan

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Re: How to under expose a screen?
« Reply #2 on: January 15, 2013, 09:43:59 AM »
Squeegee side.

I agree, I thought for sure I'd have some slime.

Offline alan802

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Re: How to under expose a screen?
« Reply #3 on: January 15, 2013, 10:48:00 AM »
Ok, now there could be several things at work here.  Is there any possibility that the squeegee side could have slightly been pre-exposed to UV light?  Maybe your light source is doing a better job than you thought and you can dial back your exposure times a good bit, or perhaps there is something wrong somewhere along the chain of events.
I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it -T.J.
Those who expect to reap the blessings of freedom, must, like men, undergo the fatigues of supporting it -T.P.

Offline Gilligan

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Re: How to under expose a screen?
« Reply #4 on: January 15, 2013, 11:15:16 AM »
Possibly pre exposed... the screen did sit out on the unit with the lid up for a pretty long time.

But we have almost ZERO UV as the weather is retarded out here and we have rain forecasted till next year it seems.  Didn't even attempt to post expose outside like I typically do.  40 degrees, wet and gray.

Offline Orion

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Re: How to under expose a screen?
« Reply #5 on: January 15, 2013, 11:15:25 AM »
If your 3140 has a 1250 watt bulb, I too would think that there was some light contamination as Alan suggested, especially with a pure photopolymer emulsion.
Dale Hoyal

Offline Gilligan

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Re: How to under expose a screen?
« Reply #6 on: January 15, 2013, 01:00:21 PM »
If your 3140 has a 1250 watt bulb, I too would think that there was some light contamination as Alan suggested, especially with a pure photopolymer emulsion.

Please elaborate?

If you mean spill because it's the older style and doesn't go all the way up the sides then that's not the case as they stay in a light tight cabinet around a wall before coming out to be exposed.

Offline Orion

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Re: How to under expose a screen?
« Reply #7 on: January 15, 2013, 02:02:30 PM »
Pure Photopolymers expose very fast but with the exposure times that you used and a 1250 watt bulb, I would think the screen would have exhibited some signs of underexposure, such as delamination and "slime" on the squeegee side. That leads me to believe that there was some light contamination prior to exposure.
Dale Hoyal

Offline GraphicDisorder

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Re: How to under expose a screen?
« Reply #8 on: January 15, 2013, 02:19:29 PM »
Walk around in open light with it like we do, it will help ;)
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