"There is green light and red light. Then there is black light, which is mostly danger."

With only a scant amount of daylight penetrating the tent, the works had developed an ethereal glow.

"Once I apply the violet pigments with a brush, the surface will become gold," he said, gazing intently at the 3- by-5-meter, or 10-by-16-foot, paintings resting on wooden sawhorses. "As the light reflects it, it will change color."

His dealer Gordon VeneKlasen, who represents him with Michael Werner, interjected, "Violet has had mystical properties since the Renaissance, which has always fascinated Sigmar."

Sigmar Polke: Inscrutable master of the unexpected, Carol Vogel - The New York Times, 27 May 2007.