Annunciation, c1515-1520. The archangel Gabriels greeting to the Virgin Mary and her response is often represented on the exterior of winged altarpieces, as it signals Christs conception. Indeed, these two panels were originally the exterior wings of an altarpiece featuring, on the interior, a Madonna and Child in the center (now in Brussels) and Sts. Catherine and Barbara on the two side wings (Art Institute of Chicago). While the interior was painted in naturalistic colors to create an illusion of reality, the painter has followed a long tradition of painting the exterior in "grisaille" (shades of gray) to resemble carved stone statues in a niche.