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First off, i am a complete novice.. so please forgive me if this is a pee-wee type of question..

I recently bought a quart of Ulano QTX, i have a question.. It seems to "lock up" in the screen, no matter how long i expose it.
I called Ulano and did a step test in increments of 30 seconds, none of it washed out of the screen..

I am washing it out at dusk with a water hose..

I am exposing using ink-jet transparencies, doubled up, with a 500W halogen light, at 20 inches from the screen.. How long should i expose it?? I am at a loss...

Couple of thoughts was that i kept it in the refrigerator, at about 38 degrees constant temp.... Would that affect it?

Any help would be greatly appreciated..
Ron
 

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the temperature would only cause a possible dripping effect on the screens while drying as the emulsion starts to get to room temperature.

What type of inkjet printer are you using? are you doing anything high detail? Are you pressing the films down onto the screen with a piece of glass? did you take the glass shield off of your exposure unit?

I have a 500W halogen worklight set at about 18inches from the screen(never really measured, but that's what it says from the kit i bought). I expose SAATI HU42 emulsion on a 156-158 mesh screen for about 13 minutes for best results.

I haven't tried the Ulano QTX yet though.
Do you own a 21 step Stouffer test strip?? they are between $6-$12 online and you should place this strip on every screen you expose forever so you don't have to keep guessing exposure times.

Also are you coating, drying, and storing your screens in a lightsafe area?

These are just some questions that might help us diagnose your problem. keep in touch!
 

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Discussion Starter #3
Thanks for the response.. I dont have a stouffer strip, i am waiting on one now.. I did the aluminum foil method, sliding it out a bit every 30 seconds..
Im not doing anything high detail.. Using 110 mesh
I'm coating my screens at night, in a spare room with a yellow "no uv" light and storing my screens in a light safe box and covered so no light can get in..
I am rinsing my screens outside, at dusk, , do you think that would affect it?

Thanks again.. Ron
 

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sounds like everything you are doing is correct.

After you expose your images and remove the transparency film you should be able to see your design on the screen.
With blue emulsion the image area will look green. With pink emulsion the image area will be a very light pink.
If you don't see this you might be getting too much undercutting in your design and/or you might be exposing too long and the UV energy/light is getting through your transparency film.

What printer are you using for your films??
 

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Discussion Starter #5
i figured out with multiple trial and error, that you do not refrigerate this emulsion... I pulled it out of the frige (which was 38 degrees); let it warm up to room temp... and for some reason... it worked perfectly..
 

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Ulano QTX image area doesn't dissolve

All SBQ sensitized emulsions like QTX are pre-sensitized at the factory with a chemical reaction that bonds photo-reactive SBQ molecules to the polymer solids that link to each other when exposed to UV energy.

There is very little decay of of this bonding over time, which is why SBQ emulsions have such a long shelf/pot life.


Diazo rules don't apply

Emulsion manufacturers publish normal specifications on pot life because they know most screen makers don't measure their exposure. Diazo sensitizer breaks down as it is saturated with water that slowly changes it's ability to react completely to UV energy. This is what makes diazo exposure a moving target. If you measure cure time of a diazo stencil you coated 8 months after it was sensitized, you will have the new/different exposure time - the moving target.


Refrigeration

Diazo does not spoil like food. Yes, cold will slow almost any chemical reaction so low volume screen makers often see on the label of any emulsion to store it in an area not to exceed 85°F - so they react by putting emulsion in the only cool place they have, where at 38°F, it's 4°F from ice.

You might have gotten it too cold and froze it a little, BUT you know that didn't hurt it, because it cured and didn't dissolve. You'll answer that when you establish a base washout time.

Experience how the stencil is supposed to dissolve
To establish a base time for washout, make a very small coating (3 inch by 6 inch?), on a screen and let it dry to the touch - then take it to your washout area and time how long it takes to dissolve - if it dissolves like it's supposed to.

Don't expose it, just wash it out. That is your standard time for washout for that mesh & coating.


As Scott wrote, if you let your emulsion return to room temperature before coating it will flow easier as you coat, but more important, you won't get drips as the coating comes up to room temperature and the viscosity (resistance to flow), goes down before it drys.

Emulsion doesn't "go bad" like a vampire at sunrise, (UV humor), it begins to react differently to UV energy. If it took 12 minutes before, it might take longer OR shorter to achieve the same cure after the expiration date. Old emulsion can always be used for mesh blockout or wood glue if you don't want keep measuring how long it takes to cure. Part of that measurement is IF the lamp is aging also.

As you're teaching yourself screen making - curiosity, experimentation and judgment are your new friends, because you're hand coating emulsion and using a quartz halogen construction work light to expose your stencils. Nobody knows how long to exposure your screens to cure/harden them, but measuring with one or two exposures how long to expose so you get a solid step 7 with your new Stouffer test positive a you will KNOW the answer.


"lock up"
The purpose of UV exposure is to change the stencil from something that will dissolve with water, into something that won't dissolve or breakdown with water.

If QTX "locks up" in the mesh, no matter how long you expose, it is doing exactly what it is designed to do when exposed to invisible UV energy - cure - harden - resist dissolving with water.


Positive Failure

"If none of it washed out of the mesh", what I think you mean is your image area didn't dissolving with water, which means your positive failed you like a raincoat made of cheese cloth or you've had storage failure, and your storage area is not safe.

You know your positives aren't very UV opaque because you double them. Think about finding a way to feed the same film through your printer twice to reduce the filtering of UV energy by the double films.

Experiments
Your new job is to discover where/how your stencil is getting exposed. As soon as the stencil begins to dry, tape a dime or some of that aluminum foil in an out of the way area of your coating.

Since you covered a patch of stencil with a guaranteed UV stopper it should wash out like a dream, even if you store it for months.

Color Change
Alas, in a later post, Scott wrote "you should be able to see your design on the screen". Unfortunately, SBQ stencils don't change color because there is no 'yellowish' diazo to change as it reacts to UV energy. This is why a test positive like the Stouffer T2115 is so important to measure stencil hardness/resistance.

As much as I am pleased to read an explanation of undercutting, that is not a very good diagnosis for the entire image area not dissolving.

I also want you to resist the temptation to allow any tolerance of "transparency". Transparency assumes light will transmit through the film which is great in school for colored overhead graphs, but as a screen maker, you need UV opaque "positives".


Stouffer Scale

When you get your new Stouffer gray scale, put it on every screen you make for the rest of your life.
Exposure FAQ Screen Making Products how to measure exposure
 

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Color Change
Alas, in a later post, Scott wrote "you should be able to see your design on the screen". Unfortunately, SBQ stencils don't change color because there is no 'yellowish' diazo to change as it reacts to UV energy.

As much as I am pleased to read an explanation of undercutting, that is not a very good diagnosis for the entire image area not dissolving.

I also want you to resist the temptation to allow any tolerance of "transparency". Transparency assumes light will transmit through the film which is great in school for colored overhead graphs, but as a screen maker, you need UV opaque "positives".

ah... I didn't know that about the SBQ emulsions.. Thx for the correction. I've only used the Diazo emulsions so far. After I get through my free batch of Ulano Proclaim that I got from ISS AC I'll probably have to try some SBQ.

I also need to start calling printed transparencies Positives... that should make explaining things easier when I talk to others.

Sorry I missed you at the AC show. I talked to the Ulano guys on Saturday and sunday and they said I just missed you. I wanted to personally thank you for all the great advice and information I've received from you so far!!
 

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You're very kind, especially after I roughed you up a little. The words I choose are important to help define their purpose. That's why I keep drumming words like dissolve, cure & UV energy, etc.

Thanks.
 

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One other thing is your definition of "dusk". QTX is pretty fast, and there could be sufficient UV light adding exposure time to that screen, depending on how "dusky" it really is. I've buggered up screens with just the backlight in my washout sink using QTX or a comparable emulsion.
You want to control all of the variables as much as possible, from coating technique, through drying, exposure, and washout so that troubleshooting problems can be conducted in an incremental and linear manner. This was something taught to me by a fellow student in college who was helping me with my black and white darkroom.
 
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