Oil-based paint that has dried in a can is the only paint that can be reconditioned for reuse. Once latex or alkyd paints dry, they cannot be fixed. Paint thinner is a solvent that dissolves the oil-based paint back into liquid form. If too much thinner is mixed in, the paint will be too runny for painting. Paint thinner breaks down the bonding agents of the paint, so minimal use is recommended.
Wear a pair of rubber gloves and open the can of paint and a bottle of paint thinner.
Dribble a couple ounces of paint thinner onto the surface of the dried paint.
Stir the thinner around the surface of the paint with a China-bristle paintbrush until the paint becomes too thick to stir.
Add another couple ounces of thinner and continue mixing. Add thinner and stir the paint until you reach the bottom of the can and the paint has liquefied.
The consistency of the re-liquefied paint should be a little thicker than honey. You don't want it to drip or run like water.