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Discussion Starter · #1 ·
This is my first time with photo emulsion. I let it dry under a fan for three hours then set a 300watt bulb with a reflector on it on top of my screen and image under a piece of glass 18-22 inches high. I went to wash it out with warm water and it was going fine but then all the emulsion around it started washing out too. I was able to clear the whole screen of photo emulsion. At least I can start over.

Does this mean I have to leave it under longer or did I not let it sit to dry long enough?
 

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A lot of factors determine whether or not the emulsion was dry. Time is one but mostly it's the humidity. When I printed out of a shop in my basement my humidity was horrible and I couldn't get it below 50%. In my new shop I keep a constant 35% in my darkroom and emulsion dries in a couple of hours (I still prefer to let freshly coated screens sit over night). So your screens were probably dry if you didn't notice the emulsion being slimy or tacky.

It's most likely not enough exposure time.


Mitchell - Star Designs
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This is my first time with photo emulsion. I let it dry under a fan for three hours then set a 300watt bulb with a reflector on it on top of my screen and image under a piece of glass 18-22 inches high. I went to wash it out with warm water and it was going fine but then all the emulsion around it started washing out too. I was able to clear the whole screen of photo emulsion. At least I can start over.

Does this mean I have to leave it under longer or did I not let it sit to dry long enough?
how long did you have it under the bulb for? 300 watt is pretty low.

i always wash out with cold water too. how high did you have the pressure? even fully dryed emulsion can be blasted away with a powerful enough jetwash.

did you degrease the screen before applying the emulsion?
 

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My guess is you need more time... I've heard of people using 500 watt lights and needing to burn them for 20 to 30 min... so with you using an even weaker bulb at 300 watts, you would need even longer than them.... granted it all depends on your emulsion type and other things... but I think you need more burn time regardless.... a photopolymer emulsion will expose faster than a dual cure btw..

Thanks,
Jeron
 

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yeah 15 minutes definitely isnt long enough. my 500 watt bulb takes me 14 minutes.
make a step template and print that. (basically just a bunch of numbers and half tone patterns going down the page that you will cover up and reveal at various points) This will let figure out how long it taking to actually expose properly.

You can tell quickly if you've under exposed as when you wet the screen the emulsion will feel slimy

your emulsion remover will still work if you "overburn" afterall, your screens are going to be used in regular light, not confined to a dark room whilst printing. id assume you'd need at least 30 minutes with a 300 watt bulb
 

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Yes to a point... once the emulsion cross links itself it is done... it can't cure any more... no amount of uv rays after that will hurt the emulsion or make it harder to reclaim... so you could burn a screen for way longer than it needed to be and it still will reclaim fine..

However you need to be careful about heat from your halogen light... while to much light won't hurt anything, heat can bake the emulsion into your screen making it nearly impossible to remove....

Thanks,
Jeron
 

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I didn't see where you said a 300w "halogen" bulb. If you used a 300w outdoor flood light in a bowl reflector, you are barely putting out enough UV rich light to expose the emulsion. A halogen light has more UV output, so it will expose faster.

Your issue is 100% related to exposure time. You are greatly underexposing.

Stronger UV output = shorter exposure time

Use a 500w halogen AT THE VERY LEAST. Preferable would be a 1,000w halogen and expose from underneath. The 1kw bulb puts out a ton of heat and will melt electrical wires and fixture if you point it down.

If you don't use a halogen bulb, at least use a "Photo Flood" bulb which is very rich in UV output. Even tho they may 'look' bright, 250w to 500w PF looses UV output overtime, so replace about every 5 hours of expose time.
 

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Discussion Starter · #13 ·
So I tried it again. I let it dry for 10 hours (no fan this time). I then let it set under the bulb for 30 minutes. It didn't feel slimy so I started to rinse it under pressure and it was coming off fine. But then I started to notice that the edges were peeling. I ended up scrubbing it all off with a brush and now have a fresh screen again.

So I'm guessing I should go back to the store and get a better bulb?
 

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If you using a incandescent light like a flood bulb, large standard bulb then it would take hours and you will never expose your fully. Are you prepping the screen properly? Using degreaser and not some soap?

If your using a halogen a 500w will expose some photopolymers in 5 min. You can also get 1000 w halogen. Make sure to take the protective glass off these lights as the contain a UV filter.

Also photopolymer is humidity sensitive. If your not under 40% for a few hours before exposure its most likely never fully dry and moist emulsion will not cross link properly.

There are a lot of variables here that you need to check.
 
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