Why Does the Painting Have Doors? It Was Designed to Be Shut

The arrangement is a central panel with two narrower wings hinged to its sides, sized so that the wings meet when closed and cover the centre completely. Opening them reveals the principal image spread across all three panels, while the outer faces of the closed wings carry a separate composition, frequently painted in muted colours or in imitation of stone sculpture. The object therefore has two entirely different appearances, and the artist composed both. Larger versions with more panels follow the same principle, and a two-panel version hinged like a book was equally common and served the same purposes at smaller scale.

The format solved several requirements at once:

• •Protecting the painted surface from smoke, dust and damage when not in use
• •Allowing the image to be revealed at particular moments in the year
• •Matching the church calendar, with the closed view used in penitential seasons
• •Making a large image transportable, since the wings fold over the centre
• •Fitting a wide image above an altar that is itself wide
• •Giving donors a place, since they frequently appear on the inner wings

What is painted on the outside is frequently as interesting as what is inside and is far less reproduced. Because the closed state was the ordinary one, seen every day, while the open state was occasional, the outer painting was what most people actually looked at for most of the year. Artists used that, painting scenes that anticipate the interior, images of the donors, or figures rendered to look like carved stone, which is a deliberate illusion playing on the difference between sculpture and painting. The change from a grey exterior to a brilliantly coloured interior at the moment of opening was a designed effect and must have been startling in a dark church.

Multi-panel arrangements come in several forms and the names are worth keeping straight. A diptych is two panels hinged together like a book, used for portable devotional images and for portraits of couples. A polyptych has more than three panels, frequently many, arranged in tiers with a predella of small scenes along the bottom. A winged altarpiece may have two sets of wings, opening to reveal a second interior for the most important occasions, which northern European workshops built at enormous complexity. A pair of paintings intended to hang together without hinges is a pendant rather than any of these. And a modern artist using three panels is borrowing the format deliberately for its associations.

Several of the most important paintings of the fifteenth century are in this format and their histories are eventful. The Ghent altarpiece, completed in 1432, has twelve panels, has been stolen repeatedly, was dismantled and dispersed, was hidden in a salt mine during the Second World War, and one of its panels stolen in 1934 has never been recovered. A number of famous works were sawn apart by dealers, since three separate paintings sold for more than one object, and museums now hold panels of the same altarpiece in different countries. Reconstruction of dispersed examples by matching wood grain and panel dimensions is a recognised area of research, and several have been virtually reassembled.

A central panel with two hinged wings shows one image open and a different one closed, so the artist composed two works in one object. The format protected the surface, allowed revelation at particular moments and made a large image transportable. The closed view was what most people saw most of the year and is far less reproduced. Dealers sawed many examples apart, and museums now hold panels of the same work in different countries.