This is one that we get asked and receive comments about all the time! What is my exposure time with this emulsion and this light? How long should I expose this emulsion? Why wont my light work for exposing? Or the funniest one is "this is crap" "your emulsion sucks, I'm going to leave a bad review"
Well guys the only one that can really figure this one out is you, the printer or if it’s a large shop then the person in charge of developing screens.
There is a lot that goes into exposing a screen, it's more of a science although we wish we could give you a concrete number to follow every time, unfortunately it doesn't work like that. We need to consider the type of ink and what type of exposure unit you are using because based on this you are going to pick your emulsion. One part emulsions generally expose much quicker than those you need to mix diazo into. Making that the first exposing time factor.
Next what type of light are you using? Are you starting off using direct sun? The industry noob standard 500W work lamp? Or maybe a box style exposure unit with tube lights? If you’re really fancy and have a few thousand to spend, maybe you are using an L.E.D. unit ?
A 500 W lamp will run you $20-$30 bucks maybe less with a coupon and it will expose screens but you can be looking at an exposing time of 8-12 minutes "roughly." Now let's consider the emulsion you are using; how thick/thin are your coats? How far the screen is from the light source and so on. Now on the other end of the spectrum there is the L.E.D. units with the fancy vacuum that can expose a screen in seconds but will run you the price of a used car.
Ok so now you have that figured out. “Well I use the 500W lamp so that means I need to expose between 8-12 minutes.” Wrong! Remember it depends on a lot of factors, your emulsion, how thick did you coat you screen with emulsion, how many coats did you do? 1 per side or 2 per side? Also are your film positives nice and dark? If not, you may end up exposing a little longer to get that image to really come out, which means you are now over exposing to compensate for a crappy film positive.
So the only real advice we or anyone can give you is just a rough ball park of what exposure time “could be.” We recommend getting a step wedge test or an exposure calculator to really calibrate your exposure time properly. Both types are really easy to use. We have a simple to use Step Wedge here available for sale.
Good luck printers, remember before you turn into a hater and want to tell your current emulsion company their emulsion is crap just remember, it's probably you. Follow our advice get a step wedge or exposure calculator and remember reach out to us if you need help or are confused, we are always here to help the best we can!