Why does opaque white run slower than clear coat?

Pigment scatters and absorbs UV before it reaches the bottom of the film, and press speed scales directly with the fraction that gets through. On heavy whites this is the dominant term.

How do I find my ink's transmission?

Run a speed trial: slow the press until the ink genuinely through-cures by a rub or adhesion test, then work back. The transmission that speed implies is grounded in your ink and your lamp.

Ink cures on top but stays soft underneath.

The surface received its dose and gelled; the base did not. That is the signature of setting speed from a surface measurement on a pigmented film, and adhesion failure follows later.

Does slowing down fix a tacky surface?

Not when the cause is oxygen inhibition, which is usual. More time at the same intensity does not help; more peak intensity, an inert blanket or a surface-active initiator does.

UV Curing calculator

UV Ink Cure Speed Calculator

Find the press speed a UV ink can hold when only part of the lamp's output reaches the base of the film. Enter the through-cure dose, cure-zone length, web irradiance and film transmission.

What this calculator does

Press speed a UV ink can hold based on the dose that actually reaches the bottom of its film.

Formula used

Irradiance at the film base = web irradiance × transmission
Required dwell = target dose ÷ irradiance at the base
Press speed = (cure zone ÷ 12) ÷ required dwell × 60
Surface dose needed = target dose ÷ transmission
Speed given up to pigment = (1 − transmission) × 100

Inputs explained

Ink Target Cure Dose: Dose the ink needs at the film base to through-cure.
Lamp Cure-Zone Length: Illuminated length along travel, not the housing.
Measured Irradiance at the Web: Radiometer reading at web height, at running power.
UV Reaching the Base of the Film: Fraction of incident UV reaching the bottom of the film.

How to use the result

Best suited to setting press speed for a pigmented ink, explaining why white runs below rated speed, deriving transmission from a speed trial.
Transmission is wavelength-dependent; a long-wavelength initiator can use a window pigment leaves open. Ignores oxygen inhibition, a peak-irradiance problem that slowing down does not fix. Assumes uniform film weight; a heavier lay-down transmits less.

Common questions

Why does opaque white run slower than clear coat? Pigment scatters and absorbs UV before it reaches the bottom of the film, and press speed scales directly with the fraction that gets through. On heavy whites this is the dominant term.
How do I find my ink's transmission? Run a speed trial: slow the press until the ink genuinely through-cures by a rub or adhesion test, then work back. The transmission that speed implies is grounded in your ink and your lamp.
Ink cures on top but stays soft underneath. The surface received its dose and gelled; the base did not. That is the signature of setting speed from a surface measurement on a pigmented film, and adhesion failure follows later.
Does slowing down fix a tacky surface? Not when the cause is oxygen inhibition, which is usual. More time at the same intensity does not help; more peak intensity, an inert blanket or a surface-active initiator does.

Last reviewed 2026-10-01.