[hoobertita]

I've been lurking here for days but now joined to ask this question:

I have read that after you expose your screen, it can continue to expose if you're washing it out in a non-lightfast area. I'm operating under the assumption that when the water hits the screen, that stops the exposure. Is that right?

Its been my experience that there's a range of stuff you can "get away with," in terms of exposure. But I'd like to make sure that I understand the basic principles of how the emulsion works so that when I mess it up, I can understand what i did wrong.

 

[Twisted Grafix]

Full exposure happens when the light penetrates the emulsion layer and crosslinks it all. Finding the correct exposure time with an exposure calculator will give you the ideal time to expose.

"I have read that after you expose your screen, it can continue to expose if you're washing it out in a non-lightfast area. I'm operating under the assumption that when the water hits the screen, that stops the exposure. Is that right?"

Yes, it can expose the areas that were NOT exposed under the printed areas of the film positive.

Do not place your screen near a window for extended times when washing out because natural sunlight will expose unexposed emulsion.

Trial and error is best. We have a dedicated dark room, but wash out in a separate area. There is a window, but we do one screen at a time and don't have any issues.

Vector images are far more forgiving than halftone images as far as timing for exposure goes.

 

[hoobertita]

Thanks for your reply, very helpful.
So when i read that i should "set" a screen by leaving it in sunlight or UV light after washout, this is the process of completely crosslinking all the photoreactive bits, once the open screen areas are clear.

 

[Twisted Grafix]

You can do that after it's washed out. If you want to ensure fully crosslinking, expose to the proper time (determined by your exposure calculator test), wash out & dry. Then expose it again. You shouldn't have to do this if it's exposed properly the first time. I've never had to post expose. What emulsion and exposure unit are you using?

 

[hoobertita]

1: S.E.X. for plastisol,
2: DCM dual cure for waterbased

I use a 500w halogen at 14": for 1, 10 min; for 2, 13 min
or the sun at noon for 1, 45 sec or 2, 120 sec.

Yes. I have to pony up with an exposure calculator. I've wasted more time and energy avoiding its use than i would have spent on using it. :/

Thank you again for your expert advice.

 

[Twisted Grafix]

Anytime! That's why we're all here. Yeah, I'd get the exposure calculator to get the times dialed in. I started with a halogen light setup years ago and did the try and see what happens method myself. It can get frustrating! I finally ponied up for the exposure calculator and found the times were way off. On a side note, if you get to the point down the road that you can move up to even a cheap UV fluorescent bulb setup, you'll see a huge difference!

I am currently using an LED unit I built last January. Everything has been fine until we did a dozen screens about a week ago. Only the left edge of the screen was exposing, so I lifted the top and turned it on. All the lights worked. I closed the lid, all the lights worked...or so I thought. It turned out there was a solder connection that worked loose which made 75% of the LEDs output about half the light. Quick 5 minute fix and now all the lights are back to full intensity, and all screens are back to normal.

If you can stick with one process, it will greatly reduce the variables for things to go wrong. With your current setup, you can quickly narrow it down to a bad bulb, bad emulsion, or incorrect exposure time. The sun is great especially in a pinch, but you are limited to daylight and no rain/snow. The halogen will allow a controlled environment and will produce consistent results time after time in a dry environment day or night.

 

[hoobertita]

Control your variables..Yee buddy. That is some mad science right there. THX