Cartonnage is a type of material that was used by the ancient Egyptians for making funerary masks, outer wrappings, light-weight inner 'coffins', and decorative panels for their mummies. Cartonnage was in use from the First Intermediate Period onward, although its composition changed slightly over time.
Cartonnage was made from layers of linen or papyrus covered with plaster or resin, which formed a stiff surface when dried. It is comparable to papier-mâché, although the linen or papyrus was not pulped or folded. Instead, the material was cut into the proper shape and layered with the plaster to make a thin, light-weight board somewhat akin to plywood. This material would hold its shape indefinitely, and was much easier to paint or decorate than the linen wrappings.
Early Middle Kingdom: cartonnage made from plaster and linen was used for mummy masks; by the mid-Twelfth Dynasty artisans were producing longer masks that also covered the upper body.
Third Intermediate Period: by this point the masks had expanded to an entire inner mummy-case (at least among the wealthy). Cartonnage was generally made from linen and stucco. The mummy-cases were brightly painted and decorated. These fell out of use before the Late Period.
Ptolemaic Period: from the late Ptolemaic period to the beginning of the Roman Period, cartonnage pieces were often made from old and unwanted papyrus scrolls, although linen was also used. During this time it became common for the mummies to be covered in segments of cartonnage forming a sort of 'suit of armor', with separate plates for the head/shoulders, chest, an apron over the legs, feet, and sometimes separate pieces for the rib cage and stomach.
Roman Period: cartonnage became thicker and sturdier, leading linen to become the preferred material once again. It was not unusual to make cartonnage from alternating layers of linen and papyrus or with outer layers of linen and an inner core of papyrus. The cartonnage often took the form of a full-body box, and the head-pieces became more elaborate.
Obviously, cartonnage manufactured from old papyrus scrolls is particularly interesting. This custom has preserved a number of manuscripts in Greek, Egyptian (Hieratic, Demotic, and Coptic), Latin, and Arabic that would otherwise have been lost. These include land surveys, government petitions, temple accounts, and formal contracts, among other odds and ends. Even more interesting, some included fragments of works of fiction, including Plato's Phaedo, part of the final act of Euripides' play Antiope, and fragments of Homer's Iliad.
Hundreds of cartonnages have been destroyed looking for useful manuscripts, but unfortunately, most manuscripts are either fragmentary and/or fairly useless. Scrolls that might reach 35 feet in length were cut to the shape needed for the cartonnage, meaning that a single scroll could be split between multiple mummies, and unused segments might be discarded. Those that were used are often further degraded by time and insects. Fortunately, new recovery techniques are being developed which are less destructive and leave the stucco layer intact.
By the end of the Roman Period, cartonnage began to be replaced with painted funerary portraits and shrouds known as Faiyum portraits; these were a Roman tradition, resembling the ones found at Pompeii.