Hilma af Klint was an abstract artist before the term existed, a visionary, trailblazing figure who, inspired by spiritualism, modern science, and the riches of the natural world around her, began in 1906 to reel out a series of huge, colorful, sensual, strange works without precedent in painting. The subject of a recent smash retrospective at the Guggenheim Museum, af Klint was for years an all-but-forgotten figure in art historical discourse, before her long-delayed rediscovery.