I have built an exposure unit, with 18 inch 15W filtered black light tubes (the dark purple ones) 2.5 inches apart (four of them). The 3/8 inch thick acrylic top is about 2.5 inches from the tubes (unit's side is of 1x4's), and I am pressing the screen down with a few books on top of a black foam board piece.
I print my positives on 3M inkjet trancparencies, with "heavy matt paper" setting, 1200 dpi, looks pretty dark (lots of ink). To increase the opacity of the mask, I print two, and tape them together.
I use Ulano Proclaim, and coat each side once with a scoop coater. I dry them in a dark closet for 24 hours, relative humidity is arouond 25-28%.
The problem is that I either overexpose the screen (about 10-15 minutes exposure time), or the squeegee side doesn't get exposed enough (about 5-10 minutes exposure time). I can only make a usable screen, if I kind of underexpose, and wash it very carefully, so that washing the underexposed squeegee side would not desolve too much emulsion.
I just ordered a new batch of emulsion, as well as a 21 step exposure guide, but I am not sure if my exposure unit is not the culprit. I've read on Ulano's tech sheet, that in case of "filtered black light fluorescent tubes" I have to double the exposure distance which they suggest to be 4-6 inches normally. Well, I am way too close to the tubes, I can see that, but before I rebuild the unit, I'd like to hear some expert opinions.
Thanks a lot in advance!