The Claude glass is a slightly convex dark mirror, first used in the early eighteenth century. It is an artist's aid, named for the Baroque Rome-based landscape painter Claude Lorrain, whose use of subtly graduated tones proved very popular in the years following his death. The landscape painter uses the glass to reflect the subject of his painting, thereby softening the light and, by reducing the colour of the scene, revealing more clearly the tonal graduations to be reproduced.