Crucifixion Diptych (van der Weyden) that they could be the left and center panels of a triptych, that they formed either the wings or shutters of an altarpiece, or that they were intended to decorate an organ case. The train of the Virgin's robe continues onto the right panel, which evidences that the panels were intended to lay side-by-side rather than separated (as the wings of an altarpiece would have been). Art historian E. P. Richardson proposed that they were the center panel of the lost Cambrai altarpiece (executed between 1455 and 1459), a single painting now split into two parts. Art historian Penny Howell
Early Netherlandish painting both sides or with the reverse bearing family emblems, crests or ancillary outline sketches. In the case of single panels, the markings on the reverse are often wholly unrelated to the obverse and may be later additions, or as Campbell speculates, "done for the artist's amusement". Painting each side of a panel was practical since it prevented the wood from warping. Usually the frames of hinged works were constructed before the individual panels were worked on. Glue binder was often used as an inexpensive alternative to oil. Many works using this medium were produced but few survive today because of