“That’s it, I’m sooo done with screen printing!”
Okay, so for the last few prints, your screens came out terrible.
It was underexposed, you saw emulsion melting away during washout. It was over-exposed and can barely see through it. Fine lines in your design washed away, just like your motivation.
I get it.
You’re pissed off because you followed the instructions exactly as the label, but didn’t even come close to what you were hoping for.
Now you’re sitting here feeling frustrated for having wasted all that emulsion and time.
Fortunately, I found the solution for you. And once you’re done reading this, I guarantee you’ll be exposing professional grade screens in the next 20 minutes. Read on.
Emulsion and Screen exposure time
As it stands, there are simply too many emulsion types in the market today – some are diazo, some are single pot emulsions and the newer ones are hybrids. (Here’s a good explanation of each type)
Each one has its own unique characteristics and will work well with different substrates. Each will also require different exposure times. But here’s what I found after testing 6 different emulsion types from different companies.
Forget what the manufacturer has recommended/put on the label – often times they aren’t setup like how we are.
So whether you’re in the humid tropics of Thailand or in dry and nippy Switzerland, the only way to expose perfect screens is if you use an exposure calculator.
DIY your own exposure calculator
Before I begin, please make sure that your exposure setup is correct. For example, I use a diy screen exposure unit that consists of a flood lamp placed 2.5 feet away from my screen.
Keep in mind, in whatever setup you have, make sure to maintain the distance between the light source and screen at all times.
Any inconsistency and your calculations won’t be accurate. Here’s an overview of what I mean.
Let’s begin with Step #1.
To create your own exposure calculator, you’ll need a relatively thick, heavy cardboard (or something dark so no light shall pass). For this example, let’s use an A4 sized board.
Step #2, cut the board into 6 even sized strips. (You can mark each strip with numbers but that’s too much work.)
Once you have the strips made, Step #3 is to line them up over your screen. Make sure you don’t leave any gaps in between each strip. This is to prevent any light from passing through. See the diagram below.
Step #4 is to place the strips over your image. It’s okay to if the strips don’t cover the entire screen, but it MUST cover the entire design.
Tip: You can use some see-through tape to lightly hold down each strip in place. Finally, you should have something like the picture below.
Step #5 is the where the fun begins.
First get a stopwatch. You will start removing each strip in intervals of 2 minutes. Start from the top of the screen.
Now let’s start exposing. Turn on your light source and set your timer.
If you’re confused, do exactly as the diagrams below:
You get the point.
Once you’re done removing all the strips, move to Step #6 – washing out the screen.
What you’ll start to notice is the time/interval in which your image is exposing correctly.
If you did not get the perfect exposure, at least you’ll have a clearer idea as to which interval window you need to adjust to.
TIP: If you’re just starting out with the exposure calculator, don’t get too ambitious with a design that has a ton of details.
I like to start with a solid image with large areas with maybe a few slimmer lines.
It may take you a couple more screens and calculations, but this is how you pinpoint the optimum exposure time.
Alright that’s my pro tip for today. If you have any questions, please write them out in the comments below, I’d love to know what you found.
Hope this helps you stay motivated!