Since 1966, Japanese artist On Kawara has been producing paintings that depict only the date of their creation, executed in liquitex on canvas in eight standard sizes. If he can’t complete a painting on the day he starts it, he destroys it. Each entry in the series is painted carefully by hand in the language of the country in which he produces it; to date he’s completed more than 2,000 paintings in 112 countries, and he says he’ll continue until he dies.

Is this valuable? Yes: In 2006 Christie’s sold Nov. 8, 1989 for £310,000.