What Ad Reinhardt did was quite wonderful. The subtly different, near black geometric shapes in his paintings cam back from a show in Los Angeles scuffed. So he just repainted them and hung them up to dry.
From As I See It
Ad Reinhart, (1913-1967) also known as Adolph Frederick Reinhardt, an American Abstract Expressionist / Minimalist painter, describes his signature black paintings, which he focused on exclusively from 1953 until his death in 1967: “A free, unmanipulated, unmanipulatable, useless, unmarketable, irreducible, unphotographable, unreproducible, inexplicable icon.” These canvases—muted black squares containing barely discernable cruciform shapes—challenge the limits of visibility. Reinhardt saw his own dark canvases, with their classic, geometric compositions, monastic repudiation of anything extraneous, and contemplative depth as a fusion of Eastern and Western traditions. Reinhart's paintings are in collections throughout the world.