Washing out problems / Troubleshooting.

[tenspeed]

Hey all,

As you know, I'm still very new to this. I've just burnt and washed out my 4th screen but this time I've noticed a fair amount of the emulsion has come off. I used the same lamp at the same distance for the same amount of time as before, with the same emulsion and negative. The only differences where:

-I used a different sheet of glass (Maybe something about thickness stopping the
UV Light?)

-It was left coated but unexposed in a dark cupboard for about a week as opposed to a day / day and a half max.

My gut feeling is that maybe the age stopped it burning quite so well but I can't think of anything to back that up. What do you think?

[paul204]

If you want to know what I think:

Buy a 21 step transmission step wedge test. Put it on your screen. Follow the instructions. It will tell you how long to expose your screen.

Burn a screen with the time you found with your step wedge test with a positive. If your image doesn't wash out your positive isn't dense enough, get better film. If it washes out fine, you're in business.

[adamturman]

Keep everything consistent as well. Don't switch out your glass for example. From you description, I'm thinking it may have been that.

As long as your screen is kept in a completely dark/dry area, it should keep pretty well for quite a while, if anything it would be harder to wash out.

Make sure your film is pressed tightly to the glass as well.

Good luck!

[tenspeed]

@Paul204: I might do - I guess I was lucky that I hit gold first time with the previous set up.

@AdamTurman: I'm only printing for myself at the moment so it isn't a problem for me to recoat and simply experiment. It was - the screen was in a cupboard with a towel draped over it to stop light seepage.

Slightly off topic but I just had a look at your site. Absolutely love it - especially the Pin Up section. Thanks for the advice!

[galmiklos]

I had problems with exposure and wash out myself too, and after a suggestion from Andymac, I swapped the acrylic top of my home made exposure unit to 1/4 inch plain glass. It changed the world! Even the color of the exposed emulsion is different!

What I am trying to say is that the quality of the glass (or plastic) on top of your exposure unit seems to count a lot. No wonder. The light is supposed to go through...

[Andymac]

glass thickness and type (or plastic vs glass) will definitely affect any stencil exposures.

changing one for another will too.

Keep this in mind Nubians.....

1. UV light is what makes your stencil react and go hard.

2. anything that blocks or minimizes the UV light makes your exposures take longer, and can affect how well the stencil crosslinks and hardens.

this includes:

a) lamp type. This has been discussed ad nauseum. High output lamps (metal halide, super actinic fluorescents etc) are better than low output( blacklights, halogen, photofloods) UV is different than visible light. Less power or output = more time and/or incomplete exposure and hardening.

b) glass type and thickness. the thicker, the longer the exposure takes. the more impure or UV light blocking attributes, the longer or more incomplete the exposure

c) film positive material - the thicker and less clear, the longer it takes for the light to burn through the layers of your film. oiled paper or frosted mylar/vellum takes longer than clear film

d) thick stencils take longer to expose than thin ones - the backside facing the light may go hard, but if the light does not have time or power to expose the whole layer of emulsion, then the side away from the light (squeegee side) will be soft and unexposed. this can cause the emulsion to come right off the screen during washout.

If you go ahead and set up your exposure and use less than optimum materials during exposure, then expect to have to fuck around with things not working as well as they could.


If the information on this site is helping you troubleshoot your problems, then show some class and buy a premium membership, help support the site as we help support your efforts in screenprinting.


OK, where's the beer?

[caribou]

if your emulsion is getting old, it will take longer to cure under the lights. with the stuff i use, a fresh screen takes about 35 minutes to expose, when the jar is a few months old, it creeps up to about 40 minutes to expose.

[tenspeed]

@Andymac: I did go premium after the site helped me the first problem I had. I didn't know about the thickness of the stencil being a factor - I've been keeping it consistent so that won't be the issue.

@Caribou: I didn't know about that - I heard about it having a sort of 'use by' date before it starts going off but I didn't know anymore then that. Thanks for the heads up.

I've pretty much narrowed it down to the glass - I'm going to have to experiment / get a 21 stop indicator and figure out the new times. Every other single element has stayed constant. Cheers guys.

[adamturman]

Keep this in mind Nubians.....

1. Andymac is what makes adamturman react and go hard.

OK, where's the beer?

I got your beer right here buddy.

[tenspeed]

Amazing.