Can I put epoxy over painted lettering or artwork on an outdoor piece?

Yes, as long as the paint is fully dry and compatible.

Latex and other water-based paints are best because they dry fast. The epoxy can go over them in about 24 hours.

Oil-based paints take a long time to fully dry. If the piece was painted with an oil-based paint, apply 3 coats of oil-based polyurethane to seal the surface before brushing on the epoxy seal coat. If you go directly over oil-based paint that isn't completely dry, you run the risk of the epoxy not sticking and peeling off months later.

The same rules apply to stain on a wood sign. Alcohol-based or water-based stains are best and can be coated after about 24 hours. Oil-based stain needs the 3 coats of oil-based polyurethane first, and the epoxy must not touch any bare oil-based stain. If you pour and see any area where the epoxy pools up or pushes away, that area did not get enough polyurethane, because epoxy does not stick to oil stain and will repel off it.

All epoxy has a slight amber tint by nature. It isn't noticeable unless it's poured over something completely white, and oil-based polyurethane has the same tint. For white or light painted areas, UltraClear Art & Craft Epoxy keeps the best clarity.

Painted pieces that will live outdoors still benefit from a spray-on UV polyurethane coat after the epoxy cures.