Calibrating dot gain in screen printing

#Overview

Print an unscreened, uncorrected halftone gradient and compare it to your computer screen: the print is darker, midtones are clogged, highlights have vanished. Nothing is broken — it's the physics of the process. Every halftone dot grows between the film positive and the fabric:

1. At exposure: light bends slightly around the film's dots; the small dots of the highlights don't cure enough emulsion and wash away at rinsing, while dense areas close up.
2. At printing: ink pressed through the mesh spreads beyond the open dot — more so as the mesh is coarser, the ink more fluid, the pressure heavier.

Result: a 50% dot on the film can cover 65-75% on the print. The entire tonal curve is distorted — and distorted differently in every shop. That's why the "standard" compensation values in manuals never quite work: they describe someone else's shop.

#The answer, by measurement

Calibration Flow doesn't ask you to estimate your dot gain: it measures it. The workflow is that of your first calibration, applied to screen printing:

1. Generate the target — 25 patches of known values, from white to black. Export it as a screened positive, like a normal film positive (polarity and halftoning).
2. Pull the target through screen printing — your screen, your emulsion, your ink, your pressure, your substrate. That's the whole point: the target travels through exactly the chain your images will travel through.
3. Photograph the dry print — even lighting, no cast shadow.
4. Import the photo — the app detects the target, reads each patch's real value and plots the drift: what 10%, 20%, … 90% actually became.
5. The compensation curve is generated — it pre-lightens exactly what your process darkens. It applies automatically to all your subsequent film positives, and exports as

   .acv

   for Photoshop if you prepare your visuals elsewhere.

Recalibrate whenever a link in the chain changes: different mesh, different ink, different emulsion, different press. Curves are kept in a library — one per shop configuration.

#What it actually changes

• Highlights exist. Without compensation, everything above ~85-90% brightness prints pure white. The curve gives those areas back their dots.
• Midtones breathe. The "clogging" of the 40-70% range — where faces, skies, and materials live — is pre-corrected.
• Gradients connect. A gradient that "jumps" abruptly into a solid flat is the classic symptom of uncompensated gain.
• The run is reproducible. The curve encodes your shop; as long as the chain doesn't change, the result doesn't either.

#Honest limits

The curve compensates tonal drift, not mechanical defects: an under-tensioned screen, uneven exposure, or a worn squeegee produce variations that averaged measurement can't fix. If two prints of the same target give two very different readings, stabilize the process before calibrating — calibration freezes what it measures, instability included.

#Key takeaways

.acv