vacuum bag exposure technique

[BHart]

Hey,

I'm trying to figure out how to expose my screens. been playing around with building a flourescent tube unit, been looking into buying a new one...
I have two 500 watt halogens i used to use with glass and remember reading here somewhere that a few people have been exposing by putting the screen in those vacuum bags from target or wherever.
does anybody have a link to this discussion, or any insight. i'm curious and it sounds a lot cheaper, easier and would obviously take up a lot less space.

[boxymouse]

I've been meaning to ask about this too. A board and weights have been working quite well for me, but I suspect a vacuum would make my screens more accurate (there is a bit of screen stretch on a warped frame).

[vrooooom]

You can use the vacuum bags, but they get wrinkles that sometimes show on your finished screen. They work better if you use them as a neoprene replacement on a unit, I would imagine.

It's not tough stuff, so I tried using one and had to scrap it after about 10 uses due to holes in the seam.

A sheet of glass can be about $30-$70 depending on the size you need, and will last for years with proper use. Space bags are about $10 for a jumbo?

[BHart]

thanks vrooooom,

I like the idea of the vacuum creating direct pressure for the transparency against the screen and it also seem such a simple idea.
problems seem to be as you mentioned, wrinkles, and also the short life-span of the bags

[Aaron Gein]

I got a couple of these bags from U-Haul a few weeks ago to try it out. I've only burned two screens with them so far but they work great. You do have to deal with removing wrinkles as you vacuum air out....but it's really not a big deal. Here is how I do it....start with the bag laid out on your exposure surface with the side that has printing on it facing up, tape your positive to your screen and put foam into the squeegee side of the screen, holding the screen with the positive facing down and the foam resting in the screen place the whole thing in the bag, seal it up, vacuum out some of the air....not enough to make it super tight...just enough to snug it a bit and allow you to turn the whole thing over. Now turn the whole thing over so that the foam side is on the bottom and you're looking at the positive. Smooth out wrinkles with your hands. Continue vacuuming out the rest of the air and smooth out wrinkles as you go. Easy as can be. If you're exposing from above, turn on your light and walk away. If you're exposing from below, flip the screen over then turn on your light and walk away.

As I said, I've only burned a couple screens this way so far, but the wrinkles issue was not an issue. Will have to keep using them to be able to weigh in on the durability issue...though I image it's like most things, take care of it and it will take care of you. Another bonus to the bags is it shaved a minute off my exposure time as opposed to the thick glass I was previously using. Also no risk of breaking glass and slowly bleeding out in my studio all alone. And better screen/positive contact. And the ability to vacuum seal a screen, throw it in a black bag, and walk it outside into the sun for sun exposure. Even if it only lasts for 10 screens I'd say that for $1 per screen that's a lot of pluses and not a lot of minuses.

[vrooooom]

Main cause of wrinkles for me: I use 30x40 frames for printing. The largest size bag barely accommodates that. Other minor issues were aluminum frames cracking the corner seams, and ink/old emulsion, frame dust, regular dust getting in the bag and causing pinholes.

They're great for a quick start if you follow what Aaron mentioned. Can't beat the investment cost. But, last studio I worked at had used the same glass/exposure unit for 10 years without replacement (except for bulbs), and a conservative estimate would be 2000 screens during that time for glass that was about $100 new. 5 cents a screen ain't too bad either.

Still taking my screens outside, but I replaced the bag for a pane of glass and use a compression setup with a light integrator. Pretty happy until I find a permanent spot on the property to do the exposure unit right.

[k8bit]

I've been using them for about a year now and always get good exposures with them. Aaron covered it, the main concern is to smooth out the wrinkles. If I'm careful I can get 40- 50 screens from a bag. Holes are usually along the foam side and can be taped up without affecting the exposure area. I usually end up scrapping the bag because they start to get a little too worn and wrinkly. But my screens are max 25x36, I don't think I'd want to go much bigger with this setup.

As an added bonus, I use the old ones to vacuum seal my old portfolio cases.... My house is leaky.

[ittybittypress]

I found an off-brand space bag on Amazon a few months ago. They came 3 to a pack for $9.95 and are big enough (barely) to accommodate a 36x48" screen. I've exposed about 50 screens using one bag, haven't touched the other two yet. And I get really tiny stuff to expose with them, like the separation info that InDesign automatically adds prints clean as a whistle now. It's kinda a pain to get the giant screens in the bag, but being able to expose with the sun is totally worth it.

I believe the bags came from this Amazon shop: http://www.amazon.com/s/?ie=UTF8&key...&rnid=15899471

[billybadass]

Will this technique work with a halogen light or will it melt the bag?

[ittybittypress]

Aim a fan at it if you're worried about overheating.