I am having a terrible time getting a screen to expose correctly. I thought I had figured out a good exposure time, but after trying two more screens today, I clearly must be missing something. Let me try and provide as much detail as I can about my process and equipment I'm using.
First, I'm making my own screens out of 160 mesh. I'm using Saati Grafic PS2 Blue emulsion to coat my screens. I'm coating 1/1, so one coat on both sides of the screen and then letting the screen dry with the shirt side face down.
I will let the screen dry overnight for a min of 8 hours, but I usually let it dry for 12 hours. To expose the screen I'm just using a 500w Halogen light set 16" above the screen. Once the screen is exposed I take it outside in my backyard and use my hose to wash it out.
The other day I exposed one screen for 3 min 20 sec and it seemed to washout perfectly, so today I exposed 2 screens one for 3 min 20 sec and tried to wash it out, but the emulsion wouldn't wash out at all! So I tried the second screen for 3 min exactly, the emulsion did eventually wash out, but it took forever spraying it with a jet spray from my garden hose nozzle. Because I had to use the jet spray just to get any of it to wash out it looks like it's definitely not the cleanest washout.
I just don't understand what I'm doing wrong. I time the exposure to be exactly the same time each time, so why one day it washes out without hardly any water pressure and then the next day I can't wash it out to save my life is incredibly frustrating!
The only difference I can think of is that one day (the day that worked with very little water pressure) I washed the screen out at night versus today I washed two screens in the sunlight without much success and with one screen not washing at even a little bit!
What am I missing or what else can I try? I've exposed this same screen 7 times now and I have to do it again because the emulsion didn't wash out today despite exposing it for the same 3 min 20 sec. Any help would be greatly appreciated!