What exactly is a diptych? In short, a diptych (pronounced dip-tick) is an ancient method of recording knowledge that is defined by the presence of two separate carved surfaces which are held together by a hinge.
Various kinds of diptychs are known to exist. The one of the most common forms was actually little more that a shallow box filled with wax. A stylus was used to make notes on either side of the diptych. This way for recording information had two advantages over paper. It was waterproof, and the writing could be erased so the diptych could be used over and over. This was commonly used for teaching people how to write.
Another common form of diptych is when two related carvings or paintings are hinged together. Typically, these were religious in nature. Many men of the cloth would carry one or more of these with them to set up during sermons as a visual display for their parishioners. The sides were often folded together to easily move and/or to protect the artworks contained inside.
Although diptychs took many forms these were the two most common types of dyptychs.
The term diptych and be extended to triptych for a three paneled object or even a polyptych for one with more than three panels.