This ties in with a prior post, about matching paint. My wife found the original paint in the basement in a semi-solid state. It had the recipe on it so we can get more, but she doesn’t need much. Is there a way to turn partially hardened paint into good paint? Blender? Water and stirring? Or just buy some more?
The first thing I would try is taking it to a paint store and having them shake it. That’s what I usually do with old paint. From there, they should be able to tell you if it’s still usable. Otherwise, just have them mix up the smallest amount they can, probably a quart.
If it’s water-based paint, me, I’d add a jigger of water and stir like crazy. A blender is overkill, IMO. Add more water in tiny amounts if needed. Paint can go from “a little bit too thick” to “colored water” in only a splash, so go easy and stir generously between dilutions.
Do not fret about the chips and chunks of dried paint that will end up in the mixture. Strain the endproduct through two or three layers of cheesecloth to remove the bits. Repeat if required, or use a finer mesh, like a strainer.