diptych

thumb|Ivory consular diptych of Areobindus, [[Byzantium, 506 AD, Louvre]] thumbnail|Wax tablet and a Roman [[stylus]] thumb|Barberini Ivory, [[Constantinople, 6th century, Louvre]]

A diptych (, ) is any object with two flat plates which form a pair, often attached by a hinge. For example, the standard notebook and school exercise book of the ancient world was a diptych consisting of a pair of such plates that contained a recessed space filled with wax. Writing was accomplished by scratching the wax surface with a stylus. When the notes were no longer needed, the wax could be slightly heated and then smoothed to allow reuse. Ordinary versions had wooden frames, but more luxurious diptychs were crafted with more expensive materials.