tullawulla

I've just started to make my own stencils; I'm finding it difficult to wash out. it's requiring a power washer!!

After a few step tests 5mins seems to produce a decent result. seems too short to me.

• I'm drying the emulsion with a hair dryer before placing on a black foam pad.
• the stencil is placed ink side up with a sheet of glass on top.
• the 1000w halogen is 23inches above.
• the glass etc is 'hot' at end of exposure, wil this cause problems?

Is the emulsion to thickly applied? It's 1 coat front and back finishing on the squeegee side a la Greaves.
on the attached image i added an extra layer of vellum with design, this is to demonstrate a choke on the 'bare' stencil.
any help would be appreciated.

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Celtic

You need to let your emulsion fully dry before you expose it. I wouldn't rely on blowdrying it.
Also, yes, you can certainly cook your emulsion with your halogen.

 

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RichardGreaves

The number one job of EVERY screen maker is to learn to make an exposure test and not confuse undercutting or light scatter with overexposure.

You have diffused fluorescent lamps and haven't done what it takes to compensate for undercutting by enlarging your art yet. Undercutting makes your image smaller by choking it, you need to enlarge it to compensate. The bottle neck in your picture is the perfect choke demo.

You are also using vellum finish paper that also diffuses energy.

Undercutting
http://www.ulano.com/FAQ/FAQexposure.htm#Q2

Exposure
Exposure FAQ Screen Making Products how to measure exposure


Emulsion is easy: If the emulsion washes out - it wasn't exposed enough. If it doesn't wash out, it was exposed and crosslinked somehow. Your stencil is doing what it should - the sensitizer is crosslinking and holding in the mesh.

Water pressure will FORCE and tear the unexposed stencil. You could also smash open your front door, rather than taking the time to use the key.

Properly exposed, you can soak a stencil for hours without harm (as we do in dip tanks) to dissolve the open areas. The whole point of cross linking the sensitizer is to make the exposed areas water resistant so they won't dissolve and rinse down the drain.

We have about 500 individual posts saying that their stencil washes out and the answer is always the same. Under exposed.

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How are you measuring? retired Ulano Technical Support
Screen printing since 1979 - SGIA Academy Member

 

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tullawulla

thanks Denise and Greaves.

My stencil isn't washing out, so I'm going to
-increase the distance of the light source from screen, to reduce the direct heat
-is there a case for letting a screen dry naturally because I'm convinced it's the heat thats causing the emulsion to 'harden'.
-I understand the undercutting but my main concern is the difficulty in washing out the 'soft' unexposed areas.

I'll try another test at night when uv a is not a factor.

thanks

 

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RichardGreaves

Quote: Originally Posted by tullawulla My stencil isn't washing out, so I'm going to -increase the distance of the light source from screen, to reduce the direct heat -is there a case for letting a screen dry naturally because I'm convinced it's the heat thats causing the emulsion to 'harden'. -I understand the undercutting but my main concern is the difficulty in washing out the 'soft' unexposed areas. I'll try another test at night when uv a is not a factor

Stencil doesn't stay in the mesh
If the stencil washes out - it wasn't exposed with enough UV-A energy, so it dissolves with water and rinses down the drain; just like it is supposed to.

Image area doesn't wash out
If it doesn't wash out, it was somehow crosslinked with heat or UV-A energy.

If your problem was that the image area didn't wash out, this usually means your positive failed to stop UV energy from reaching the stencil.

Dime Complete Opacity Test
To judge if your positive completely stops UV energy, tape a dime or a piece of aluminum foil to the stencil to see if the dark areas of your positive are failing you and letting UV-A energy through to the stencil. If the area covered by the dime doesn't wash out, you have exposed the stencil to UV energy or heat energy and the stencil resists dissolving with water and going down the drain.

__________________
How are you measuring? retired Ulano Technical Support
Screen printing since 1979 - SGIA Academy Member

 

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