It has been said that singers are a dime a dozen. But great singers? Not so much. Mezzo-soprano Shirley Verrett was one of the greats. She eventually transitioned into soprano roles, transforming the rich depths of her voice into a velvety, caramel-hued spinto of power and grace. Above, Verrett sings the aria "Vissi d'arte" in the title role in a 1978 Metropolitan Opera production of Giacomo Puccini's Tosca.