Can a UV absorber rescue a pigment with poor light fastness?

It delays the fade; it does not fix it. If light fastness is the weakness, treat it as a selection criterion rather than something to patch later.

Assess first. Draw the pigment down in the target base, expose it under xenon or UV for 24–72 hours, read ΔE and compare visually. Above ΔE 2–3 the change is visible, though the acceptable threshold is the product's to set.

Then the mitigation, in three layers: choose an inherently light-fast pigment, since inorganics — iron oxides, chromium oxide green — generally outperform organic lakes; add a UV absorber to cut the energy reaching the pigment; and use a coating or treatment to lower photocatalytic activity at the surface.

Be clear about the limit. A UV absorber slows a fade that is inherent to the chromophore; it does not stop it. For products that live in light — a compact carried in a bag, anything left in a car — light fastness belongs in the selection brief from the start. We hold a range of light-stable water-soluble colours for exactly this need, with test data available on request.