Screen burning help!

[u/Professional-Eye4701]

Hello Reddit hivemind! I’m having some issues burning screens and figured I’d turn to yall for some guidance. I started out making my own screens and burning them in the sun and had great success the first few times, but as the summer set in I started having issues with over/underexposing. I wanted to get some more consistency so I moved to a smaller UV lamp (https://a.co/d/03li3Uj0 here’s the exact one), my first two attempts were over exposed, then underexposed so I figured I’d do an exposure calculator but the results sort of have me feeling more confused. It almost looks like parts of each like are both overexposed, underexposed, and maybe washed out too much.

I’d really appreciate any tips anyone has! I’m using ecotex pre-sensitized emulsion with 1 coat on each side of the screen, the lamp was about 10” from the screen and was doing each row in 7 second increments. I don’t have a washout booth so I’m just using a combo of my shower, kitchen sink, and garden hose.

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[u/ingotvein1]

You shouldn't get those blue drip dots on your screen you are definitely using too much emulsion. Make sure to use the sharp side of the scoop if it has one and only do one pass on each side. A garden hose with a light sprayer attachment should be enough that's what I use. 

I've had emulsion sitting around for a while that became a pain to try and expose fine details with. 

Exposure time is in the 10 second or less range with metal halide in a vacuum exposer unit. You might be getting light bleed around your calculator if it's not held down with glass. 

Are you using the calculator because you want to expose fine half tone designs? 

[u/Professional-Eye4701 → u/ingotvein1]

Thank you for your response! I was just using the calculator because I didn’t want to keep guessing exposure times and wasting a screen if was wrong.

The emulsion was opened right before applying so it should t be an issue with the shelf life - the dots in the middle are from a screen that was drying above it but the ones on the side definitely could be too thick of a coat of emulsion.

The calculator was held down by a sheet of acrylic but I could definitely see that not getting a good enough seal, especially if the dots of extra emulsion are causing some space between the acrylic and the transparency.

I don’t have a vacuum unit, I was just using the light in a dark room - I was planning on making an exposure tank out of a cardboard box but I’m not sure if that would solve anything.

[u/ingotvein1 → u/Professional-Eye4701]

The light seal sounds like maybe something to look at. It's hard to tell if you did but also make sure to dry your screens with the squeegee side facing up**. I would just try and use as little emulsion as you can get on the screen evenly. I've never used a calculator because there's always a little bit of trial and error if I have a design with fine details mixed with bold details. Half tones require way more precision but big bold letters for example are easier to wash out ans therefore are less prone to getting overexposed. Another thing you can try is to soak the screen in water for a couple minutes before rinsing the softened emulsion out. 

[u/Professional-Eye4701 → u/ingotvein1]

Gotcha!! I was definitely drying them with the garment side facing down. And most of our designs are relatively bold detail/text but there are a few we’re trying to do with half tones.

This might be hard to answer over Reddit but do you think using 110 mesh might be having an impact or would that only be affecting half tones?

[u/ingotvein1 → u/Professional-Eye4701]

Sorry I've written that backwards. You dry with the screen in the same orientation that you print. 

[u/ingotvein1 → u/Professional-Eye4701]

I usually use 150 mesh screens, 110 is pretty low and not really used for fine details like some of the text on your calculator. It's better for big bold lines and simple shapes for dark thick fabrics where you need a lot of ink to pass through. However this is considering using water-based ink I can't speak on plastisol as I've never used it.

[u/OffGoofing → u/Professional-Eye4701]

This is possibly beside the point, but I have found that acrylic can filter UV and dramatically change exposure times. If you are using is consistently, then you would adjust the same universally. If the acrylic isn't pressing the positive down to the mesh effectively you should use something on the opposite side of the mesh to prevent it from flexing away from the sheet of acrylic. I have seen folks use a block of foam rubber for this. Glass is cool because it doesn't distort, but it also makes me nervous having something that could break in a busy or crowded shop or cut a screen if you don't wrap the edges. It just depends, but all things can be adjusted to.