In her steel-rimmed glasses and beaded chiffon dress, the little old lady looked like a tintype grandmother. Her birdlike, smiling face was framed in a white lace collar and black ribbon choker; on her feet were pointed little one-button shoes. But there were surprising touches too: as a guard for her wedding ring she wore a blue celluloid chicken band, and one ear had a bright green dab of paint.
Grandma Moses was getting ready for her 88th birthday and for her tenth anniversary as a professional artist. In those ten years she had painted some 1,300 pictures, which now sell for...