Time does not treat paintings well. Old paint tends to become contaminated when exposed to the air for a long time, and it ends up fading the work to the point of being unrecognizable. But NASA looks to have figured out a way to bring these paintings back from the dead.
The method involves removal of organic contaminants from the damaged art-pieces using atomic oxygen. Without affecting the actual painting, the process removes all organic matter like carbon or soot.
The paint is not damaged as the pigments in paint are mostly inorganic and have already been oxidized. Besides this, the organic pigments can also be preserved by carefully timing the exposure to atomic oxygen. It also does not affect the canvas as it only reacts on the surface of the painting.
As for the results, well, I think the image above speaks for itself. On the left we see the painting after "the Cleveland Museum of Art staff used acetone and methylene chloride to clean and restore the painting." On the right, the painting after NASA was through with it. Not too shabby.