Screen printing exposure calculator, free printable
A free printable exposure calculator for screen printing: a test film of 2 to 8 timed zones plus the cover-and-expose schedule, as one PDF made in your browser. Find the right time in one test.
Faster with the free Chrome extension: right-click any picture on a website and send it straight to the exposure calculator. Add to Chrome · what it does
Extension installed. Right-click any picture on a website and choose Makerfern → Open this picture in… to bring it here.
One screen, several exposure times
Getting exposure wrong is the most common reason a screen washes out soft or loses its detail, and the right time depends on your lamp, emulsion, mesh and how thick you coat. An exposure test answers it for your setup: set the times to try, print the film, follow the schedule, wash out, and pick the zone that held.
What is on the film
- Halftone patches at 10, 30, 50, 70 and 90%, at the line screen you print, drawn as solid vector dots.
- Fine lines from 0.25 to 2 pt, and small text from 5 to 12 pt.
- A solid block, to see how large areas wash out.
- The time of each zone, and a 1 in ruler to check the print size.
Making the art itself? The halftone generator turns a picture into print-ready dots at the same line screen.
Questions
How does an exposure calculator work?
It is a film with the same test marks repeated in several zones. You expose the whole film, then cover the zones one at a time, so each zone gets a different total time. After washing out, the best zone is the shortest time where the emulsion has fully hardened and the fine lines, small text and light halftone dots still open. That time is right for your lamp, emulsion, mesh and coating.
What times should I test?
Start from your emulsion's data sheet for your kind of light, and bracket it: the shortest zone well below, the longest well above. The default is 60 seconds to 3 minutes in 30-second steps. If the answer falls between two zones, test again with a smaller step around them.
How do I read the result?
Underexposed zones feel slimy on the squeegee side, lose colour when rubbed, and fine detail washes away with the emulsion around it. Overexposed zones hold the stencil but the finest lines and the 10% dots fill in. The winner holds everything that is also on your real films.
Does the printer matter?
Very much. The film is only a test if its black stops UV light. Print on transparency film at 100% on the darkest setting, and hold it up to a light: if you can see through the black, print two and stack them. The ruler mark at the bottom shows whether the printer shrank the page.
What is the mirror option for?
Some printers put the film printed side down, touching the emulsion, which gives the sharpest edges. Mirroring the film makes the marks read correctly that way round.