Step Test: Finding your exposure time
Exposing screens is tough, every set up is different and it's easy to miss something. With a step test as long as you check the key points below, you'll find your perfect exposure time, for you set up, your environment and the equipment you have.
Key points to check:
- Transparencies. Hold it up to a light, it if it not blocking it, it won't work.
- The transparency is flat and tight to the screen. Foam one side, thin glass the other works best. Need foam?
- The screen is evenly coated with emulsion and is completely dry. A scoop coater really helps here!
If you're good on the above, let's carry on!
So your overall exposure time will be different depending on how close your light is to the screen, how powerful your light is and what brand emulsion you are using. If there are manufacturers guidelines on light distance from the screen, follow them, it will give you a starting point. If you need a bit of guidance on this, drop us a line and we'll try and give you your best starting points.
For this example we're going to say that we estimate the exposure time to be about 13 minutes. But we'll test from 8-18 minutes, because we're not totally sure and want to make sure we find out!
Take a screen, mark on the wood, on the side you'll have the transparency, a line every inch, lengthways. You could masking tape and mark the tape if you don't want to mark the screen.
The idea is that we are going to cover the screen with something that will not let light through, a large piece of black card works well, as you can maneuver this under the piece of glass. We will use the card to allow various parts of the screen to be exposed for longer than others.
As we're testing from 8-18 minutes, on the screen, give each inch mark it's own unit of time, starting at 18 minutes, working down to 8 minutes.
Hopefully by now you can see where this is going!
Set your timer for 18 minutes counting down. Cover everything apart from the 18 minutes band. Switch your light on.
When the timer gets to 17 minutes, slide the card down and allow the 17 minutes band to start getting exposed.
Every minute move the card down until your last band is exposing, it should have 8 minutes to run at this point.
So you've now got a screen with 10 different levels of exposure. Time to go wash it out.
You'll find that some wash out too easily, some don't wash out at all but wait.. what's that one that washed out perfect?
It's your perfect exposure time, for your set up, in your environment.
If it looks like your in between say 9 & 10 minutes. Go burn a screen at 9.5 minutes.
Got a question? Give us a call on 01752 656 336 or email us firstname.lastname@example.org
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- Tags: emulsion timings, screen buring timings, screen burning, screen printing exposure times, screenprinting exposure