One of the fragments analysed in Table 1 (E25416) shows exceptionally high calcium and also a quite high sulfur content levels. X-ray diffraction analysis of the surface of a sample revealed the presence of calcium sulphate in the form of gypsum. Also zinc (not reported in Table 1) is to be found in this fragment, but the relevant compound was not identified. Electron microscopy of that sample confirmed the presence of sulphur and calcium, and showed that the zinc was localized in submicron grains attached to the calcium sulphate. The presence of these two compounds in these fragments remains unexplained.
analysis of organic elements
C. papyrus L. contains native starch, which is situated around the conducting fi-brer. The form in which starch is found in papyrus used as a writing support is an important key to know how papyrus was manufactured in the past.
Our method was to cut sections using a freezing microtome, stain them with lugol for study under the optical microscope23,24. We analysed two types of ancient papyrus.
• Papyri dating from between the 3rd century BC and the 8th century AD, which mostly came from papyrys cardboard (i.e. several sheets stuck together); given by the Sorbonne Institute of Papyrology.
Altogether, fifteen papyri were thus examined under the optical microscope, and classified into three categories.
• Starch was totally absent in three of the samples from the Sorbonne Institute of Papyrology (Sorb. 1, Sorb. 3, and Sorb. 6). The various restoration treatments to which these objects had been submitted could explain this observation.
Fig. 3: Section of papyrus Copte 1. Left: A longitudinal section of the conducting fibers with the burst starch grains on the surface. Right: Transversal section of another fiber. The endogenous starch appears darker and can be seen as grains inside the papyrus and as starch on the surface (x 190).
۰ Seven papyri only contained endogenous starch (A2, A6, A7, Copte 1, Sorb. 2, Sorb. 4, and Sorb. 7). These samples must, therefore, have been manufactured without the addition of a starchy glue.
۰ The density of the starch grains varies greatly among the papyri. This can be explained by the age of the C. papyrus L. stem when it was harvested and dried by exposure to the sun. Two of the papyri were found to have grains of starch that had burst due to thermal effects experienced over the centuries (Fig. 3).
۰ A starchy glue was found on five of the papyri (A3, A4, Copte 2, Copte 3, and Sorb. 4). Two of these (A4 and Copte 2) were made of three layers (Fig.4), between which glue was found. In these cases, the starchy glue was found in the join of two sheets of papyrus from the same scroll. Wheat and barley flours were identified in the glues. Indeed, the size of the intact grains looks very much like these cereals. In two other samples (Copte 3 and Sorb. 4), a starchy paste was found on the surface of the papyrus. They came from the Sorbonne Institute of Papyrology and were found as papyrus cardboard, made from many layers of papyrus stuck together.
Fig. 4: Section of papyrus A4. Three layers are visible. A starchy paste (darker area) has been used between the two layers (x 190).
Finally, we analysed a join from a Greek papyrus (A3), in which a starchy glue was also used. Some of the very small starch grains remained intact (2 mm x 4 mm in size) but these cannot be attributed to any known starch (Fig. 5).
Thus, it became obvious that no glue was used to stick together two papyrus layers during manufacture. Starchy glue seems to have been used only to stick two sheets of papyrus to make a scroll or to make cardboard at a later date.
Cellulose and lignin
Papyrus is mainly composed of holocellulose, comprising cellulose (54-60%) and hemicellulose, and of lignin (36-40%)13 their proportions determined by location and season.24 These polymers are organized according to different morphologies (α-, β-, and γ-cellulose).
The problem is to find out whether the relative proportions of these components can be used to characterize a papyrus and determine its state of preservation. To examine this hypothesis we have analysed by thermogravimetry papyri from different epochs and various geographic locations25
Thermogravimetry analysis is a simple, rapid and reliable method requiring a small sample. It involves monitoring the loss in mass of a material as a function
Fig. 5: Section of papyrus A3. Left: the black vertical band corresponds to a starchy glue. Intact grains can be observed near the center of photo (x 470).
of temperature (dynamic analysis) or as a function of time at a given temperature (isothermal analysis). The change in mass corresponds to a range of physical and chemical processes, which can be used to characterize the various components by studying their degradation curves. In the case of a composite material, such as papyrus, dynamic analysis has proved to be the most useful.