# Symptoms of over exposure and under exposure?



## ryanellsworth (Jul 5, 2012)

I'm pretty new to screen printing and am trying to get exposing down as well...I have symptoms of what seems like both under and over exposure, pretty confusing. 

I am using a uv black light exposure unit I just built with 4 tubes about 6" from the glass. Using ulano qx-1 and qt-discharge I followed the recommended BL times on their site, and my first try gave me what looked like a solid step 14. WHAT?? Well I guess it makes sense, since it was hard to wash out and reclaim.

So I cut the time in half to 100 seconds for qx-1. Now it looks like I have a solid step 12, however the image washed out pretty easy and turned out pretty good. But the ink side of the screen was slimy, which I thought is caused by under exposure. 

I am doing one coat on each side as well as scraping off excess emulsion...any advice? Am I over exposing? Under? 

Also not sure if I'm even reading the steps right, since some of the steps are more see through? Does solid step mean solid not washing out or solid the same color as the rest of the emulsion?

Pic:


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## PhilR (May 3, 2011)

It's always best to rely on proven results with your own setup than focusing too much on prescribed times. If your screen washes out fine but is still a bit slimy then try increasing your next exposure a bit. It takes a few real jobs before you find the sweet spot.


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## knifemaker3 (Sep 8, 2006)

Not sure about the emulsion you are using as I've never used it before.

When I started out I was using the pink crap ryonet sells. One day I took a chance an ordered some chromablue emulsion from Atlas screen supply.

WOW! I can expose screens in 11 seconds, doesn't require to be in a light bug bulb room ( regular flourescent bulbs to light room is fine) and is easier to wash out. 

Question, are you spraying both sides of the screen and letting them set for a few seconds before washing? If so, it seems that you will have more troubles with the slimy screens than if you just lightly spray both sides and then start immediately washing them out. Or at least it does for me when using chromablue. Again, your emulsion may be different.

From your picture I'm wondering if you aren't getting too thick of a coating. Are you using the sharp or dull side of your scoop coater? Are you using a scoop coater or applying by hand? If you are using a scoop coater try using the sharp side and slightly tilt it backwards before starting to coat. Hard to explain, but look at your scoop coater. It should have angles on the ends. to use properly you tilt the coater to the screen until you see the emulsion forming a solid line across the bottom of the screen, then tilt the coater back slightly so that you are only moving the line of emulsion across the screen and coat. If you do not tilt back slightly you will be applying a large amount of emulsion making a very thick coat, even if using the sharp edge side of the scoop coater. This thicker coat will be more difficult to work with and can cause the slime you are describing.

Just a thought to consider....


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## ryanellsworth (Jul 5, 2012)

Yeah I have been spraying both sides and letting it sit for a minute or 2, then spray both sides again and let it sit for a minute, then it starts coming out. Apparently the screen is underexposed though since you can see the steps 4-12.

I have been having trouble getting the scoop coater down as well, I use the dull side and push the angle part up against the screen. This does do too much because I'm always scraping a bunch extra off. And sometimes when I do it a big part of the screen won't even get covered, maybe I've been pushing too hard? I will have to try angling it back a bit more.


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## knifemaker3 (Sep 8, 2006)

Seems like ryonet had a good video on using a scoop coater on youtube at one time. You might try looking it up.

Try using the sharp side of the coater. It works better unless you are needing a thicker stencil.

If it is taking you that long to wash out your screens you are getting them overexposed. You shouldn't need to let them sit for more than 30 seconds before starting to wash them out. I don't let mine set but immediately wash the ink side until I start to see the design and then flip around and finish washing it out on the shirt side. Then I blot it dry with paper towels and sit the screen horizontally in front of a fan to dry. Doing it this way helps keep any water and loose emulsion from running down the screen and into the design plugging it up.

Good luck and keep practicing!


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## ryanellsworth (Jul 5, 2012)

UGH is there anything more frustrating than not being able to expose a screen? Another failed attempt tonight. It doesn't help that I have to wait 24 hours between tries. According to Mr. Greaves my screens are underexposed... for example in my pic in the OP it's only a 3 since you can see 4 and above. 

I don't get why when everyone else does the test their exposure step is easy to see, one totally solid and the next washed out. I get these weird half baked in between steps that won't rinse out but will rub out.

ANYWAY so I started over with the recommended exposure time, using qt-discharge, I tried the dime test, and it took about 2 minutes for the dime spot to wash out. My screen exposed super unevenly this time, some parts would wash out and some wouldn't at all. I don't think it was the coating since when I did it I held it up to see through it and it looked all smooth and the same color. >:[


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## RichardGreaves (Nov 7, 2006)

So, do you have a second picture of your 21 Step Scale after you exposed it for the Greaves prescribed 4X of your initial exposure that cured up to 3 or 4?

If your storage isn't UV light safe, that could "crust" the entire surface of your stencil like a photographer "flashing" photographic film.

*Establish a base time for development/washout*
Every stencil mesh, coating thickness, emulsion & water are different - so you should test.

Make a very small coating (dollar bill size), on a screen and let it dry - then take it to the sink and time how long it takes to wash it out.

Don't expose it, just wash it out. Don't let it sit for this test. Watch the clock as you develop the screen. Average screens don't take longer than 1-3 minutes at most. That is your standard time for washout for that mesh & coating.

If you have areas of the screen that are hard to budge, you know they were crosslinked somehow and your room is not safe for stencil storage


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## ryanellsworth (Jul 5, 2012)

Heres another picture, this is with a different emulsion but I am having the same problem, where the image is taking a long time to wash out or parts aren't washing out at all. This time the screen wouldn't wash out at all hardly and almost all the smaller details were totally burned into the screen. I went 8 min this time, from 2:30 before.


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## RichardGreaves (Nov 7, 2006)

Looks like a Solid Step 11. 5 steps more than you need to resist chemicals.

Different emulsion, different volume of exposure energy needed.


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## knifemaker3 (Sep 8, 2006)

Are you using a pressure washer or just a regular garden hose? Use a pressure washer if not already doing so.

I still think from the looks of your posted pics that you are getting too much coverage of your emulsion. I know when my employee coats screens he gets too much on them and they won't hardly wash out correctly. That's why I don't let him coat screens anymore!


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## ryanellsworth (Jul 5, 2012)

I don't have a pressure washer, just been using the shower to rinse it out. I've read that it should rinse out pretty easily without too much pressure (if it was done right). I would like to get one though, I've been looking for a cheap used one.

I'm not sure about the coverage, it seems pretty thin to me but hard to know what it should really be like. I tried tilting back a little like you said when coating which helped a lot with making an even coat. I scrape over it again with the coater, using some pressure to remove excess, making sure its not adding any more. And hardly any comes off. That seems like it should be making it thin enough. I did forget to use the sharp side though. I am going to try again at just a little more than 1/4 of the time and see how that goes.

Edit - heres a better picture of the same screen that might give an idea of coating thickness.


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## knifemaker3 (Sep 8, 2006)

While I use just regular spray from a garden hose almost exclusively when washing out exposed screens, I have been know to use the power washer to lightly hit the design with a little more pressure when I have a screen that is a little overexposed. It's just something you learn with experience....some things like halftones you use very light spray, and other's like big open spot colors you use heavy spray. With a pressure washer you can go from very light spray to just slightly harder than regular garden hose. It does help occasionally.

I still think that you are either getting too much emulsion or like Greaves has suggested you are getting uv light partially exposing your screens.

Do you have good contact between the screen and your glass when exposing? Do you weight it down or just let it sit on top? Do you have a hold down lid or vacuum lid? 

The suggestion with the power washer really should only be used with experience. Stay with the regular garden hose for exposing right now.


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## ryanellsworth (Jul 5, 2012)

Happy to report I had much better success cutting the time way down. Tried 2:05 and the screen washed out great, a few little details were still not really rinsing out so I'm thinking I need to cut down the time a little more still. I guess I was pretty close before just a little underexposed, my dumb mistake was starting over at the recommended time. It looks like the step test was showing I was way over exposing before. 

As for the weird see through ish looking steps, I think it was a mix of being wet (once dry the steps turned more opaque) and that there was a little bit of light still getting through a crack in the door and pre exposing my screen a little bit. I put a towel over the screen now as well while it dries to help block out the light.

So yeah my burn times are about 1/4 of what ulano's site recommends for black light. I guess my box is way powerful for a black light box!


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## RichardGreaves (Nov 7, 2006)

The 21 step will measure how complete your cure is, not the clock.


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## ryanellsworth (Jul 5, 2012)

Well heres a pic of said screen, burned for 2:05. It was still overexposed but washed out pretty well. What is strange is the next one I tried 1:30 and it was a bit slimy on the inside. And actually didn't wash out quite as well as the one at 2:05. When according to the steps in the pic I should be exposing for around 30 seconds. Which can't be right. Also I am using 12 pt fonts and .25 pt lines though and some parts aren't washing out. I think I need to use a 230 mesh instead of the 160...


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## sben763 (May 17, 2009)

160 is fine for a .25 line Your exposure calculator should give a number to multiply or divide by to get perfect time. With a 1/1 coat and a 160 I'm at about 1:30 For a solid step 7. 2:00-2:30 min for a 2/2 depending on mesh. When washing out I have a clean white pad I spray both sides. Lightly hit the shirt side and little more aggressive on ink side. Spray again wait 30 sec and it spays right out. I never did this for 4 years, read it on the forums and tried it once been doing over a year now. Makes halftone screens a breeze to wash out.


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## ryanellsworth (Jul 5, 2012)

sben763 said:


> 160 is fine for a .25 line


Oh really?? I've read from a few places that you shouldn't do less than a 1 point line on a 160 mesh...however I will be printing light colored water based ink on a dark shirt so hmmm...the pad idea sounds pretty good, what kind of pad exactly? Would lightly rubbing it with your hand work?


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## sben763 (May 17, 2009)

For water base I would use a 230 then. A white chemical pad. Sold at most screen printing suppliers. They also sell at most home stores. Make sure it is non abrasive there are some that contain a grit embedded on pad.


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## sben763 (May 17, 2009)

I went by Menards this morning and they sell non abrasive white pads. White because they are the least abrasive. I use red when reclaiming and dehazing. I use to spray and wait 2-3 min and wash out even with a solid 7 on calculator seamed the emulsion got soft. By lightly hitting the shirt side and scrubbing the ink side a little harder it breaks down the unexposed emulsion much faster and the exposed emulsion doesn't soften.

Spray the hit the lightly hit the shirt side right away then the ink side. If stubborn re wet and scrub only ink side.


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## Tj Ryonet Tech (Jul 28, 2008)

30 seconds can be a big jump when you are working with lower exposure times. Try moving in 15 second increments instead.


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## ryanellsworth (Jul 5, 2012)

Cool thanks for the ideas guys. For the mesh count, is there a reason 230 is better for water based ink? I thought the ink would dry faster in a higher mesh and its best to go with the lowest mesh possible. Would it be easier to hold a .25pt line when exposing a 230 mesh compared to a 156?


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## sben763 (May 17, 2009)

I can hold that line on either screen. The reason I would use 230 over 160 with water base is the ink is much thinner and you'll get a crisper when printing with thinner inks. I use higher mesh when thinning plastisol for the same reason.


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