This article describes the conservation treatment of two black-form triptychs painted for the Rothko Chapel in Houston, Texas. An account is given of the commission and the history of the whitening that has plagued the surface of the murals. The problem was identified through a study of the artist's materials and techniques as demonstrated in simulations of the originals, comparison of preparatory drawings with patterns of disfigurement, and scientific analyses of the white exudate. The conservation process is described and suggestions are offered for the future preservation of the triptychs.