I don't remember having this problem for the first 40 or so posters I did but in the last year it keeps cropping up. I tile inkjet transparencies from my HP photosmart letter-size printer. When a couple of them overlap and if I've cut something out with scissors I'll often have a line that doesn't expose completely in the emulsion under the edge of the sheet. So I go batty patching up my screen with tape before I print.
Just add on exposure time maybe? The emuslion is new and it's happened with a couple different bucketloads now...
My "exposure unit" is a 500w halogen utility lamp.
"what are you using to hold the film onto the screen?"
ulp... either ordinary scotch tape or nothing. My exposure unit is a camera tripod with a lamp in its crotch, lamp facing downward. It goes over my screen, emulsion-up with acetate over that. So you think it might be cause the film isn't held tight to the screen?
it washes out when it should not. As though not enough light is penetrating the edges of the film. So when I print I have fine lines of ink on the paper, they kinda look like long papercuts. Then the patching begins.
The edge of film refracts the light in odd ways sometimes. It's very common to see exactly where your film ends on the screen. It usually looks like little dashes or a very thin line. Sometimes increasing your exposure time will fix this. You should start blocking out your screens before you print.
more exposure/better lamp will help. but I get it sometimes even with a long exposure.
backlit washout or put it up on a window. Get some good blockout. I use this killer Saati W-1, works pefect with waterbase, reclaims easy, doesn't start leaking during the print run. a small plastic 'squeegee' (cut a piece of those vinyl letters sticker downer things or even a credit card) will allow you to cover an edge with a thin layer of block real quick.
Thanks Andy. Your advice saved my ass in the past on exposure timing, btw.
yeah, I'm thinking I need a better lamp. The halogen ain't cutting it. But it didn't seem to be a problem early on... is it possible that the bulb is dimmer than when it was new? I've used it for about 55 posters, times an average of 4 colors equals, times ave 16 mins exposure comes out to about 3500 minutes of bulb time...
I can paint blockout on with a little brush for the tight spaces, right?