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Old May 27th, 2019 -   #5 (permalink)
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Default Re: Exposure Problems complete bust

Originally Posted by Ricks2524
OK folks, tried again using brand new Diazo Emulsion by Ecotex. Coated the screen last night. Dried for over 12+ hrs. Burnt on my calculator as per their instructions. Wash out was a no no. Bottom blew out completely. Upper portion was almost impossible to clear. I couldn't get an image except so very small places. I had to use high pressure and scrub with stripper just to reclaim the screen. Please, I ready to quit. My screens are 120 48T and they were just recently stretched.
Use the sharp edge of the coater, as that scrapes more emulsion off the screen than the round edge. You may need a room, or a "box," in which you can lower the humidity via heat and/or dehumidification.

Also check to see that the light is falling evenly over the target area. Sounds like one end exposed but the other did not. Maybe thicker emulsion on one end? Maybe the position/aim of the light favoring one end over the other?

Most of us went through this frustrating bit just as you are. Slow emulsion, weak light, no humidity control ... virtually all beginners start like that. Those things are the only reason it is hard. Change as many of those things as you can, or it will stay hard, or impossible.

For context, my first exposure unit was a DIY with 4 UV tubes. It was fairly weak, but stronger than your worklight. Diazo emulsion. Sloppy, too thick, uneven emulsion application. "Drying" in a garage in Oregon. I still have one of those screens as a souvenir. It is ruined. Partially exposed emulsion tends to get permanently locked into the screen. Unexposed or fully exposed are not a problem, but partially exposed (weak light, too thick, not dry enough) emulsion ruins the screen.

People on here were using Saati PHU and building DIY Metal Halide exposure units and heated drying boxes, so I did that too. I haven't had a ruined screen since. It takes 24 second to expose a screen. Oh, and I started using the sharp edge of the coater and got quite a bit better at getting a thin, even coat laid down. That last bit is a little bit of skill easily acquired with practice/experience--all the rest is simply having the right equipment and materials.

At present, you probably need to focus on making sure the emulsion gets dry enough and isn't too thick or uneven. Get a $10 humidistat so you know if that is a problem, and how much of a difference heating the area (or whatever) makes. I would also ditch the Diazo for a fast poly emulsion. All those steps are cheap compared to acquiring a strong light source. You can make a weak light source work, but not if the emulsion is of less than ideal thickness and dryness.
How To - Calculating Exposure Time

Last edited by NoXid; May 27th, 2019 at 11:52 PM..