What do you use to seal acrylic paint on wood?

You can use polyurethane, ModPodge or just about any varnish you choose. I like the polyurethane because it dries quickly and it pretty durable.

Acrylic Paint Sealer

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Try a polyurethane from a hardware store. The finish should be strong enough. You may be unsuccessful however, because the wooden beads were not sealed before applying the water based paint, so there is nothing for the paint to stick to.

Polyurethane. You can get it in a spray can in your choice of finish. Gloss, semi-gloss, or satin. You also have a choose between oil based and water based. If it's for decoration and not getting dirty I would use one coat of water based. If you need it scrubbable than use several coats lightly sanding with 240 or higher paper between coats. For ultimate water protection use oil based.