Cavaliere d’Arpino’s Perseus Rescuing Andromeda (1594-5)—a very small painting—is marvelously dramatic. It shows naked Andromeda pressed against a rock, a vicious sea monster approaching, and brave Perseus flying in on Pegasus. The scene is meticulously painted except for the water and sky, which is the deep and dazzling blue of lapis lazuli. Literally. This is a painting on stone. The Saint Louis Art Museum acquired the work 20 years ago, and its beauty inspired the museum to study and collect other stone paintings. The practice began in the 1530s, when Italian artists used slate and marble for paintings of sacred images. As the century turned, artists expanded their stones, using onyx, alabaster, agate and more. In this unique exhibition, 70 works by 58 artists are on view. —Elena Clavarino