Thanks to Mark!

Yoko Ono
Cleaning Piece

"Cleaning Piece,a new work which consists of a pile of stones (river rocks) in the center gallery, a large white canvas on one end wall, a large black one on the opposite wall, and an instruction on the wall in the center. Gallery-goers are invited to attach sorrows to the black canvas, happinesses to the white. Various writing materials are provided for this purpose. For each entry on the canvases, happy and sad, one removes a stone from the center pile and places it on the happiness or sadness side."