Limits In Detail?

[valkyrie]

Hi All!

So i've been hearing from sources all over that it's hard and/or impossible to get high detail out of a 500 watt halogen work lamp exposure unit, even with glass over top. I had burned my second emulsion screen ever a couple days ago, an ambitious image given that it's full of pin stripes, very tiny lines and fine details. But I had to try it. So I did. And it washed out just perfectly!!! High, glorious detail!

What I did was I rigged up an "exposure press" by cutting pieces of black foam-core to fit inside the inkwell side of the screen to be exposed (it doesn't need to be solid, I used scraps for some of the inside layers, just make sure it's evenly sturdy), with a bigger piece on the bottom the size of the screen frame to let it sit nicely. The stack that fills the inside of the screen is *just a bit* higher than the inside of the screen. Not too much! Then, take your lined up and taped film positive and screen, set it on this thing, put your glass over top (mine is out of a picture frame that happened to be the perfect size, just remember to clean it first!) Then took c-clamps with padded feet, just use those "furniture" felt pads from the dollar store, and carefully clamped the whole thing together, just enough to make a tight seal. Don't crack the glass! I was using Ryonet's WBP hybrid emulsion, a 156 mesh screen, THREE prints on Rite Film all lined up (because my new printer is a horrendous disappointment) and exposed for the suggested 13 mins (I left the glass in the lamp, but I cleaned it well before use). It took a bit to wash out the finer lines with a kitchen sink sprayer, the smallest if I had to eyeball it looks like about 0.25pt, a little less when printed, but it seriously came out beautiful.

So now I don't know *what* to think about limits in detail when using an overhand exposure unit!!! I'm curious what everyone elses' experiences are with varying level of detail with different exposure units? What's the best detail you've ever gotten out of your rig? What was your most overambitious disappointment? What's the finest line you've ever printed? Does anyone else have any home-brew mods to their rig?

I look forward to hearing everyone's stories!!!

I'm fairly obsessed with seeing how fine I can go, now. Soon I'll be burning my business cards on a 230 mesh using the same rig, which involves very teeny tiny type. I'm not exactly expecting success, but I *have* to try it. We'll see how that goes.....

-Val

[Catspit Productions]

Hey that is very cool. The truth of the matter is the 500 or 1000 watt work lamps are what we would call in the screen printing industry a point source exposure unit. This means all of the light that cures the emulsion through the film positive comes from one point light source, one bulb.

This is well known to give much better results with detail and halftones. So the work lamps are actually by their very nature good at exposing detail. The issue would be the sandwiching of the film positive to the emulsion on the screen. You seem to have seen the need to address that very issue in what you described. It would seem that your actions allowed for a nice sandwich and the film positive was snug enough to the emulsion to get off a good burn.

Now the denser your film positive, the better this would actually work as long as you don’t heat the emulsion too much during the exposure.

You should post a couple of photos of your set up as you described above. I’m sure everyone would appreciate that. I love how you say “I have to try it” because that is so true with screen printing. You never really know what you can pull off until you try.

I use an industrial black lamp multiple bulb vacuum exposure unit with a photopolymer emulsion. The photopolymer is faster than that of a dual cure as you use so the exposure latitude is much smaller. I know I have done process work in the past working at other shops with the same type unit on 355 mesh and probably a 65 to 80 lpi set up, who knows now...LOL. I have not done anything recently other than like 45 lpi halftones on 200 mesh. And normally I can burn 1 point lines on 110 mesh easily. Great post and I cannot wait to hear what everyone else has to say.

[Shamax]

Heya Val, I was in much the same boat when it came to hearing about the limits of using an overhead halogen for exposure until I actually went to try it for myself as well. I had a request from a friend to print some cloth patches with really fine lines in the design and wondered if I would be able to pull it off. I decided to go with a 156 mesh screen, 2x 8.5"x11" positives lined-up together (from FedEx Office), dual-cure emulsion, and a $10 piece of non-UV replacement glass from Hobby Lobby. I didn't use any black foam or anything on the inkwell side, though. I loaded the screen, centered, and marked it; then I aligned my positives (tape on the edges) with the center line I made on my platen, and lowered the screen to get it all lined-up & attached right. I then remove the screen from the press, flipped it on the platen so the film positive side was facing upward, and placed the glass on it. I then secured my 500w halogen exposure light in the press (it's a Ryonet starter kit), plugged it in, and kept a directional fan blowing across the whole setup to try to mitigate heat and help prevent the emulsion from baking too much. Here's a pic of what my grim and clandestine setup looks like in action



12 and a half minutes later, I turned everything off and washed out with the bathtub faucet. I was surprised at how well it all came out, actually!



I've got some other designs made up, including one with a lot of poor-man's halftones (used the "Newsprint" filter in GIMP, then auto-traced the output in Inkscape), so I'll be curious to see how well that comes out. Once I find out, I'll post here