How long to expose emulsion

July 23, 2019 1 Comment

How long to expose emulsion

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!

Later guys,

Spd




1 Response

Jay Kean
Jay Kean

January 12, 2020

SPD, having a good product is dependent upon good instructions and why your product might not suck, as you appear to be snarky about it, it would be useful to have a better set of instructions, especially for us beginners, who know nothing and aren’t a smart as you. IKEA like instructions are great for bookcases but emotion not so much. I need a simple graph give me 250 watt LED to 500 watt LED and what a typical exposure rate might be. That might be my starting point to use an exposure calculator which requires the number of seconds you think it will be and then you can do some division and expose 10 different sections to see what a good exposure might be but little old beginner me needs a starting point for your emulsion with a typical light I might buy as a robotics mentor trying to try silk screening our robot number for a competition on strong nylon fabric we use for bumpers. I ordered a 350 watt bulb but got a 250 watt for some stupid reason. Not worth sending back. The product has a 35 second exposure time in a table table at 5K light source. Since I’m not in the biz I have no clue what that is – the sun? I’ve never heard of a 5000 watt light bulb. You need to be specific. I have two screens one for the actual image I want to do and when I’m going to use the first time around for the exposure calculator. You may think it’s easy and cheap the just do as many screens as you need to trying to figure out exposure. well, I don’t have that kind of time, I’m trying to build a robot with 30 students. See FIRST Infinite Recharge. I could try to extrapolate but I still need a starting point. one review has 25 to 30 minutes for a 350 watt light bulb. That reduce has been posted in numerous places so either it’s a really diligent customer or one of you guys posting it multiple times. So I guess I’ll see if I get a reply tomorrow. BTW if I figure 25 to 30 minutes is proper for hey 350 watt LED and I might figure 40 is okay for it 250 watt. If I use the calculator out 10% time would be about 6 minutes and 100% would be 60 based on multiplying the number of seconds bye 1.5 and then taking 10% of that as your time to expose for each section of a screen calculator so once you get to row 10 you’re exposing roughly 60 minutes total. Which seems a lot based on the 5000 lightsource taking 30 seconds or so.

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