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In this third and final instalment, Andrew Greg shines a light on some of the terms and materials you may come across on Art UK, and throughout the art world.

You can read part one here and part two here. See also the Art UK glossary.


Copper sheets (sometimes called copper panels) provide a very hard, smooth surface, ideal for small detailed paintings, usually for domestic consumption. Its popularity for paintings ran alongside its availability for engraving plates, and some paintings use old printing plates. Other metals such as silver, tin and zinc have also been used.

Butterflies and Other Insects

Butterflies and Other Insects 1661

Jan van Kessel the elder (1626–1679)


Fresco is a technique rather than a material, but was the medium of some of the greatest paintings in western European art history. Fresco means ‘fresh’ in Italian and involves painting with tempera on fresh wet plaster. As the plaster and paint dry together they bind into a long-lasting surface (experiments with painting in fresco in the damper climate of northern Europe met with failure). 

Wood (often called Panel)

Most surviving paintings before the early sixteenth century are on wooden panel, as can clearly be seen on this example (below) in the Victoria and Albert Museum, where the carved framing is lost. In northern Europe oak is the wood most commonly used; in Italy it is poplar. But many other types have also been used. After the introduction of canvas and well into the nineteenth century, wooden panels were commonly used for smaller paintings, particularly when fine detail was required.

Diptych and Triptych

A diptych is a painting in two parts (from the Greek for ‘two’ and ‘fold’). Most commonly these will have been small religious paintings or altarpieces for private use. They are usually hinged and fold like a book. The outer surfaces may also be painted. One of the most famous examples in Britain is the Wilton Diptych in the National Gallery.

In a church setting a multi-section altarpiece is more likely to be a triptych, in three sections. The two outer sections, the ‘wings’ or ‘shutters’, are hinged to close and cover the central panel. Normally the wings would be closed and only opened on feast days or special celebrations.

The Deposition from the Cross

The Deposition from the Cross 1518/1519

Joos van Cleve (c.1464–c.1540)

More complex altarpieces are known as polyptychs and usually have a series of smaller paintings along the base – the ‘predella’. Over the centuries many of these complex structures haven been dismembered and the parts found separately scattered among museums and collections worldwide. Some modern artists have adopted the formats to make multi-part works, like Francis Bacon’s Three Studies for Figures at the Base of a Crucifixion and Matthew Cave’s Fort Grey Sunsets: Diptych 1.

Andrew Greg, National Inventory Research Project, University of Glasgow