Photographs from the National Gallery of Art

Scientific tests on “Ecce Homo,” left, and “Mater Dolorosa,” the central section of a devotional work attributed to Albrecht Bouts’s workshop, indicate that the two images were not meant to be seen together but were combined centuries later. Experts say that “Mater Dolorosa” was painted around 1500, 25 years before the “Ecce Homo.”

Tests of this 15th-century diptych by Hans Memling, pairing “Virgin and Child” with “Maarten van Nieuwenhove,” a client, showed that the artist painted over his original landscape in the window to Mary’s left to insert the Nieuwenhove coat of arms.

(by courtesy of The New York Times)