Exposure
test film

How to run the test

1. Print the film at 100% on transparency, with the densest settings your printer allows. Grey film ruins the test before it starts.
2. Coat and dry a screen in your usual mesh, the one you set above. Test one mesh at a time; a coarser or finer mesh will want a different time.
3. Lay the film on the screen and cover every strip with an opaque card. Download the cover card above if you want one with the slide marks and times already on it — print it, glue it to a cereal box, cut it out.
4. Expose for the base time, then slide the card down to the next mark and expose for one step. Repeat until every strip is uncovered. Each strip has now had exactly the cumulative time printed on it.
5. Wash out gently and let it dry, then read it in good light.

Reading the result

You are looking for the strip where the fine lines and the small halftone dots are fully open, and the solid areas have not started to break down. That strip's time is your exposure time for this mesh, this emulsion and this lamp.

• Underexposed strips feel soft or slimy, lose detail during washout, and the stencil may break down mid-run.
• Overexposed strips hold the solids beautifully but the fine lines and small dots are closed up or missing entirely, because light crept under the film edges.
• The right strip is usually the last one where the smallest open dot still washes out cleanly.

If every strip looks underexposed, raise the base time and run it again. If every strip looks overexposed, lower it. Note the winning time on the screen with a marker — and write down the emulsion, mesh, lamp distance and coating method with it, because changing any one of them changes the answer.

Why one film beats five screens

The usual method is to coat five screens, expose each for a different time, and compare. That costs five screens, five coatings and most of an afternoon. A step exposure test does the same job on one screen, because the sliding card gives each strip its own cumulative time.

The trade-off is honest: the strips share one screen, so a coating that is uneven across the frame can muddy the reading. Coat carefully, and read the strips near the centre of the screen if the edges look different.

What it does not tell you

This test finds the exposure your setup wants. It does not tell you which dots your mesh can physically hold — that is what the step wedge measures, and the two answer different halves of the same question. Run both once, write down the results, and most washout problems stop being mysteries.