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Exposure Problems complete bust

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Old 3 Weeks Ago May 26, 2019 4:03:44 AM -   #1 (permalink)
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Default Exposure Problems complete bust

I've been having problems with exposing, I got a calculator. Coated my screen, let dry 24 hrs. I have 500 w halogen light source approx 24 " above the screen. Burnt the screen, ( about 25 minutes total ) Then washed out entire calculator image area. . Could my emulsion be bad? Its a 2 part Diazo probably a couple months or more. What Gives. Any ideas
 
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Old 3 Weeks Ago May 26, 2019 7:10:31 PM -   #2 (permalink)
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Default Re: Exposure Problems complete bust

Yes, Diazo emulsion starts to age once mixed. Lifespan depends upon temperature, but two months is too long for Diazo regardless.

Make your life easier and get a photopolymer emulsion, like Saati PHU. They expose faster, there is nothing to mix, and they are supposed to last at least a year from the date of manufacture. I used my last bucket for over two years before I used it all up. Keep it in a cool place (not freezing).

Bad emulsion is no doubt your main problem, but I'll rattle off a few more that might be making life harder than needed.

- You've taken the glass out of the worklight, right? That glass is there to protect your eyes from UV, so you want it gone for our purposes.

- Depending where you live and time of year, it can be difficult to get screens dry enough. Humidity should be under 50%. You can check this with a cheap $10 humidistat from Home Depot. You may need to use heat and/or a dehumidifier (I do in Oregon).

- Thick emulsion does not like to dry (or expose) all the way through. Thicker is not better. Especially when you have slow emulsion (Diazo), weak light (worklight), and are subject to mother nature's humidity whims.
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Old 3 Weeks Ago May 27, 2019 1:21:49 AM -   #3 (permalink)
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Default Re: Exposure Problems complete bust

Thanks, you confirmed what I was thinking. The emulsion was thick and after 24 hours some spots still seemed wet., Humidity is also a factor that I need to work on. Thanks for the advise
 
 
Old 3 Weeks Ago May 27, 2019 5:23:02 AM -   #4 (permalink)
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Default Re: Exposure Problems complete bust

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.
 
Old 2 Weeks Ago May 27, 2019 11:30:11 PM -   #5 (permalink)
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Default Re: Exposure Problems complete bust

Quote:
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.
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