The Building Conservation Directory 2020

115 C AT H E D R A L COMMU N I C AT I O N S T H E B U I L D I N G CON S E R VAT I ON D I R E C TO R Y 2 0 2 0 METAL, WOOD & GLASS 3.3 HISTORIC WINDOW GLASS MICHAEL BRÜCKNER W E TEND to take the use of flat glass panes for sealing window openings for granted, but for many applications glass used to be unaffordable. Animal skins and other translucent materials were still widely used as substitutes for glass in windows until industrialisation gradually reduced the costs. Historical documents from the 18th century describe how complex it was to process the thinly shaved animal skins required, illustrating just how valuable glazing must have been then. One of the earliest paintings that shows how glazing was used is the Merode Altarpiece which was created around 1425 by the Master of Flémalle. The triptych brings the story of the Annunciation into contemporary scenes of everyday life in the Netherlands. In the central panel the Virgin Mary sits in a relatively prosperous domestic interior lit by a window with glazing in the upper lights only: the lower lights are unglazed, closed only by the casement shutters (Fig 1). Next door, Joseph is depicted in his workshop with shutters alone. By the time this was painted, fully transparent glass panes had been available for several centuries, but glass Fig 1 The Merode Altarpiece by the Master of Flémalle around 1425: on the left the window of a relatively wealthy family is shown with glazing in the small fixed lights at the top, while the unglazed lights below are closed with wooden shutters alone, as are the windows of the craftsman’s workshop on the right. (Photo: Metropolitan Museum, New York)