# How sensitive is Emulsion to light??



## worm (Feb 2, 2009)

HI ery body,
I have a quick question, I have been shooting screens with a 40 sec exposure time and have had everything work out great, but now that I have to wash my screens outside....I'm having issues. I expose my screen in a dark room, then after the 40 seconds, I spray it lightly with a spray bottle filled with water. I normally let it sit for about thirty seconds before I start washing out. (this is all done inside the dark room), then I run outside as fast as I can and spray the front and back of the screen with water, I repeat this several times before I actually start spraying out the design with more forceful water pressure. So my question is: How time sensitive is the emulsion(Ulano)? At what rate will it cure? I even tried cutting the exposure time in half (20 sec) and still had the same problem. It's like the emulsion is curing faster than I'm spraying so I lose detail cuz I have to spray it so hard. Too many ruined screens!! Please Help!!!


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## Solmu (Aug 15, 2005)

You use UV energy to expose screens. Sunlight contains massive amounts of UV energy.

How sensitive is emulsion to light? In liquid form, not very. In dried form, very.


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## midwaste (Apr 8, 2008)

You shouldnt need to run back and forth, you should be able to spray the screen with the bottle, let it sit for 30 secs-1 min and begin washing it out. However, direct sunlight contains lots of UV, so it would post-expose the screen while washing out rather quickly.

What are you using for an exposure unit?


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## RichardGreaves (Nov 7, 2006)

worm said:


> I have been shooting screens with a 40 sec exposure time and have had everything work out great, but now that I have to wash my screens outside....I'm having issues.
> 
> I expose my screen in a dark room, then after the 40 seconds, I spray it lightly with a spray bottle filled with water. I normally let it sit for about thirty seconds before I start washing out. (this is all done inside the dark room), then I run outside as fast as I can and spray the front and back of the screen with water, I repeat this several times before I actually start spraying out the design with more forceful water pressure.
> 
> ...


You asked lots of questions, but forgot to tell us which emulsion.

You forgot to tell us your exposure unit.

If you are exposing for 40 seconds, imagine the sun is 10 times stronger = 4 seconds. Maybe just 5 times stronger.

Lose detail means fine lines won't wash out. Do you use diffused fluorescent lamps? That means *undercutting* could be 'choking' your finelines. 

Do you have an *opaque positive* and strong *vacuum* to press the positive against the stencil?

How are you measuring your exposure?
Exposure FAQ Screen Making Products how to measure exposure

Start developing at night.


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## torodesigns (Jun 24, 2007)

What you can do to limit the sunlight on the screen from outside light is buy a trash can that has a lid on it and after you expose and spray the screen place it in the "tcan" begin to wash out in the "tcan" (trick is to open the lid at a minimum to not let the light come in). Once you see your design wash out, then you can take it out of the can and concentrate really washing out the design. Use to do it this way when I printed in the garage without a washout booth.


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## Unik Ink (Nov 21, 2006)

Yeah, I don't worry too much about ambient UV light from fluorescent lights in my shop when exposing and washing screens. I just turn off the lights at that end of the warehouse. I definitely wouldn't let sunlight hit them before I washed it out though. Sunlight will expose your screens very quickly.


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## out da box (May 1, 2007)

Surprisingly, I don't really have a problem with pre exposure even though we have warehouse flourecent lights on and sometimes our liftgate is open to the sunlight. My screen see light about 10 seconds before we expose, but they expose fine.
As for the sensitivity question- emulsion is made to be sensitive to light, some more than others.


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## worm (Feb 2, 2009)

Thanks everyone, much appreciated.

Unfortunately I don't know the name of my exposure unit. It is a German import you see and a name is not to be found ANYWHERE, believe me I've looked hard. The only reason I think it's german is because all of the breaker switches are written in German, same with the door handles, and the bulbs are from Holland. There is 7 15W fluorescent bulbs in there, glass sits about 2-3 inches from the bulbs. No vacuum unit yet (in process) and I just use Ulano waterbased ultra fast exposing emulsion.


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## RichardGreaves (Nov 7, 2006)

worm said:


> 7 15W fluorescent bulbs in there, glass sits about 2-3 inches from the bulbs.
> 
> I just use Ulano waterbased ultra fast exposing emulsion.


15w lamps means your unit is as weak as you can purchase, and much, much weaker than the sun (10x).

All emulsions are waterbased, so you _might _mean water resistant. No matter what sensitizer your emulsion uses, you should learn the product name so it is easier to re-order.

I hope you are using ultra fast QTX with your lamps, but you still should learn to measure exposure to make sure the stencil is completely hardened/cured. 
http://www.ulano.com/FAQ/FAQexposure.htm#Q1

The suggested QTX exposure time for 40watt Black Lights (BL) on 305 mesh is 60 seconds. You are using much weaker lamps and (I assume), lower, coarser mesh - so your 40 seconds is under exposed.
http://www.ulano.com/emulsn/presensitized.htm#qtx


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## worm (Feb 2, 2009)

Thats exactly what puzzles me, Now I don't know if bulbs are made differently in holland, but with my 15W bulbs, I have exposed screens in as little as 10 seconds! If you ask me, this thing was not originally cheap. I have worked with big, expensive exposure units that still take 60 sec to expose a screen. And I do know the name of my emulsion, however I am always looking and trying different types to get everything TOTALLY zoned in. Trust me, I know what your saying though, 15W sounded weak to me too, but this thing exposes screens waaaaaaay fast. ANYWAY, thanks to the reply's, I was able to figure out that I was indeed unintentionally exposing the screen with ambient light. So after the advice, I was able to expose what I think to be a pretty hard screen to expose. None the less, I thank you kindly for replying to my question


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## RichardGreaves (Nov 7, 2006)

*Exposing emulsion w/15 watt lamps?*



worm said:


> I don't know if bulbs are made differently in holland, but with my 15W bulbs, I have exposed screens in as little as 10 seconds!


OK. 10 seconds works for you. Which lamps & emulsion so people can learn & compare?

Are you getting a solid step 7 on a known international standard Stouffer 21 or 10 step gray scale?









If there is sensitizer that hasn't been cross linked, the stencil hasn't been completely cured/hardened.








Like crust on toast or steak, exposure is like filling a bucket w/water. Screen makers can *only expose one side of the stencil*, so it is important for the UV energy to _move through the stencil_, all the way to the back, where the squeegee blade will rub the stencil where it is weakest.

How are you measuring?


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## worm (Feb 2, 2009)

*Re: Exposing emulsion w/15 watt lamps?*

According to the Stoufer scale, I do indeed wash out at step seven, at least for most standard graphic prints. I am using Ulano QFX Ultra fast exposing emulsion. It's interesting you brought up The depth of the UV penetration, that is something that I was not thinking of and could very well have to do with some of my exposure time confusions and my loss of detail around some tight edges. I am going to experiment with the CSC, and other exposure tools that can help me determine if I am indeed penetrating the emulsion all the way through.


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## tdh646 (Jan 28, 2009)

What if you wash outside in the shade, like under a deck or terrace?


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## Solmu (Aug 15, 2005)

tdh646 said:


> What if you wash outside in the shade, like under a deck or terrace?


If you wash in daylight, UV is a consideration. Less UV is less of a problem, but since any UV can be a problem, you're still contending with a problem.


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## RichardGreaves (Nov 7, 2006)

*Re: Exposing emulsion w/15 watt lamps?*



worm said:


> According to the Stoufer scale, I do indeed wash out at step seven, at least for most standard graphic prints.
> 
> I am using Ulano QFX Ultra fast exposing emulsion.
> 
> ...


Yes, you are using a very fast and very expensive industrial halftone and fine detail graphics printing emulsion for use with solvent inks. This is a Ferrari to the corner store. Overkill for textile work and with low energy, diffused, fluorescent lamps, you won't be able to render fine line halftones.

You should try solvent resistant QLT for textile work, at about half the cost.

The Stouffer step 7 does tell you that UV energy has penetrated all the way through the stencil and cured/hardened all the way to the inside. That's the reason to use it on every stencil you make for the rest of your life.


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