A step test answers a local question: which of several times works best for this emulsion, mesh, coating, light, positive, contact method, and washout process?
Start from an educated base time
Use the emulsion technical sheet, the exposure-unit maker's guidance, or the last time that nearly worked. The base is not the answer; it is the lowest time in the bracket you are about to test.
In the calculator, enter the base time, the added interval, and the number of zones. A 30-second base, 10-second interval, and five zones produces 30, 40, 50, 60, and 70 seconds on one screen.
Expose by moving an opaque mask
- Coat, dry, and prepare the screen exactly as you would for production.
- Place the positive in firm contact and mark the test zones so you can identify them after washout.
- Expose the full test area for the base time.
- Cover zones 2 through the final zone, leaving only zone 1 open, and expose for one interval.
- For each remaining interval, uncover one additional numbered zone: expose zones 1–2, then 1–3, and continue. Keep the final zone covered during every added interval so it remains at the base time.
- Wash out, dry, and inspect the stencil only after following the same development process you use in production.
Choose a usable zone, not merely the easiest washout
Look for a stencil that is fully hardened and holds the detail your job needs. A soft, slimy stencil or edge breakdown points toward underexposure. Closed fine detail or stubborn image areas can point toward too much exposure, poor film density, or poor contact; change one variable at a time.
Chromaline's published step-test example uses this same progressive masking pattern. Its guidance also emphasizes that shop conditions change the correct time, which is why the worksheet records emulsion, mesh, coating, and light.
When to run the test again
Retest after changing emulsion, coating technique, mesh color or count, film output, contact setup, light source, lamp distance, or a condition that changes UV delivery. Also retest when normal screens begin behaving differently instead of compensating blindly in washout.
Primary method reference: Chromaline, Dial In Your Exposure Time