I'm at a loss!!! I'm trying to expose a 160 mesh screen using a 500 watt lamp. I've tried various times, from high to low, all with the same result... the image does not wash out!!!
I bought an exposure calculator but the only thing that washed out on the exposure calculator were the halftone grids and the letters, but none of the measurements gages ranging from 1.0 - .25.
I don't know what i'm doing wrong. Could my emulsion be bad? I mixed it at the end of May so it's been about 5-6 weeks since it was mixed.
What type of emulsion are you using? How long are you letting the screens dry? What temp are they drying at? Sounds like over exposure, makes it hard to wash out. Are you getting the screens wet on both sides and letting sit for 30-40 seconds.? Have you tried a pressure washer?? COuld be many things perhaps bad emulsion.
I would strongly reccomend spending some money and invest in an exposure unit though. One with a lid if you can afford it. I have a 3fx2f exposure unit purchased from RYONET. I opted out for the lid and made my own but now would have liked to have bought it. I just make sure that there is enough wieght on the foam board I custom made for it.
GOod luck...
Oh yeah are you making sure your art work and screen are flat?? if any light passes through will make it hard to wash out. Also what type of film are you using. Make sure your transparancies are opaque enough. Try doubling up if not.
I'm using DXP emulsion. Screens are drying overnight at approximately 80 degrees. I am using a pressure washer to wash out the screens.
I have thought about getting a better exposure unit but for now i'm forced to use the one I have. I can see the image on the screen, it just won't wash out!! So far i've run through 5 screens trying to get it right. When I used the standard 110 mesh, I would let it expose for 15 min and it would wash out. I even did an 80 mesh for 30 min and it washed out fine. For some reason when I use the 160 mesh, I get all the problems.
Man sorry I could not help you more. I know the fustrations I am still learning this as well. I tried exposing a screen like 5 times before I got it right a while back. Was extremely fustrating but I am starting to realize my errors are in drying time and proper exposure time.
Good luck hopefull someone else will chime in. But yeah a nice exposure unit will drop your time a lot. I exoposed a yellow screen I believe 260 mesh or something like that in 3 min. washed out almost just looking at it.
One last thing I can think of are you coating the screen to thick????? Try less time under your current lights and see if it makes a difference. I know that mesh count = different expose times.
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Re: exposure frustration
i exposed my image for about 8-9 minutes and that works for me... washes out good!!! try it.... you might not be letting it expose long enough... don't know.. trial n error.......
On most 500 watt lights the glass on them is has a UV filter, Its so when people working on cars or whatever they don't get sun-burned. It might help, If you haven't already, if you pop that filter off.
hi look I had a lot of problems exposing at the start using a 500w halogen lamp there are loads of places selling 1000w halogen lamps with frames on eBay and so forth calling them screen exposure units I have read a lot on exposure times and different bulbs and most of the companies selling halogen exposure units are recommending 20 to 25 mins with a 1000w bulb coating 1 on 1 so your 500w bulb will prob take longer again. If you're looking to make money printing shirts then it's all about timing if you have to expose four screens 25mins each then you're wasting a lot of time and money. I am amazed how some people say they can get 3 to 4 minute exposure times with a halogen lamp it just seems imposable to me. Don't get me wrong I know they work just there are a lot better options available if you're on a budget I ended up buying a 600w metal halide bulb and from a cold start I get a 4min exposure time these bulbs aren't expensive mine cost me £70 you could prob get one for about $100 it will save you a lot of time and frustration and will prob make you more money in the long run. Here's a good article on different exposure units hope it helps.Exposing Direct Emulsions --- Three Key Exposure Variables: Lamps, Time and Distance
A 500 watt halogen light place 16 inch away on a 110 coated once on both sides using standard dual cure diazo emulsion should only take about 13 min. a 1000w light will cut that time down to 2 or 3 min. but a metal halide light would be the best for exposure time
When I expose a 110 mesh with that configuration, I expose for 15 min and get a good result. I exposed an 80 mesh screen for 30 min and got a good result. The issue is with the 160 mesh. I have tried 13, 11, 10, 9, and 6 minutes and all were over exposed (i'm assuming since the image wouldn't wash out). I guess i'll have to keep trying until I get a better exposure unit.
There should be no significant difference in exposure times between 80, 110 and 160 mesh screens, maybe a few minutes at most.
I currently use a 500W halogen with Ulano QX-1 and get a good exposure at around 18 mins for 110 and 155 screens.
Try burning using the same settings on a 110 or 80 screen. I'm betting your emulsion is bad/old, although 5-6 weeks isnt that long.
Do you have a fan cooling the glass/screen while burning?
exposure frustration 
