Testing exposure

Start from the time your emulsion’s data sheet or your exposure unit’s maker suggests. (That’s general practice, not a figure from our sources.) Then use either test, and repeat it for every mesh count you use.

Method A: exposure calculator

The method Printavo and ScreenPrintingNow describe.

1. Do one long exposure, about twice your starting time, through an exposure calculator film.
2. Wash out and pick the step that looks best.
3. Multiply your test time by that step’s factor. Example: 74 s × 0.6 = 44 s.

Method B: 21-step wedge

The method ScreenPrinting.com’s help center describes.

1. Expose a 21-step wedge at your starting time, then wash out.
2. ScreenPrinting.com targets step 7 on its 21-step test. Adjust the time and test again until you reach it.
3. Keep using the wedge in daily production to catch drift.

Reading the result. Under-exposed stencils feel slimy or tacky on the squeegee side after washout, and fine detail washes away (Chromaline). Over-exposed stencils won’t open fine detail at all. Keep a log of times for each emulsion, mesh count and light.

Ulano’s rule for optimum exposure: the emulsion reaches maximum color density, with no softness or sliminess on the squeegee side.