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X-ray fluorescence spectroscopy, micro X-ray diffraction and micro infrared spectroscopy), which provided information not only on the elemental, but also on the structural and molecular composition of the inks. To differentiate between the signals coming from the inks and the papyri, the analyses covered two-dimensional areas, covering both the letters and surrounding papyri. These areas ranged from the millimetre to the sub-micrometre scale and revealed the heterogeneous compositions of the inks.
Expectedly, it was found that in 11 of the 12 analysed red inks, the colour was due to hematite (Fe2O3). Lead (Pb) was also detected in 10 of these 11 red inks and in three carbon-based black inks. However, instead of being present as red lead (Pb3O4) or lead white (Pb3(CO3)2(OH)2 and/or PbCO3) used as pigments since Antiquity Pb was remarkably found in complex mixtures that were associated with phosphate, sulphate and carboxylate ions.
The distribution of these elements was even more surprising. It was discovered that the hematite is present as coarse particles, while the lead-based compounds were found diffused into the papyrus cells, sometimes wrapping the cell walls at the micrometre scale. This creates a coffee-ring effect around the hieroglyphic signs just as if they were
outlined. This entails that Pb may have been present in a finely ground and maybe even in a soluble state; moreover, suggesting that when the inks were applied to the papyri, large particles of hematite stayed in place whilst smaller lead-based particles diffused in the papyrus, around the letters (Figure 82b and 82c).
These results imply that Pb was added to the ink mixture not as a colourant but as a dryer, which ensured that the ink stuck to the papyrus, and that it was made according to a complex recipe. Therefore, it can be hypothesised that there existed workshops in ancient Egypt that specialised in manufacturing inks. Connections can be made between these ancient ink recipes and painting practices developed many centuries later during the Renaissance. In fifteenth- century Europe, when artists rediscovered the technique of oil painting, they were faced with the challenge of drying the oil within a reasonable amount of time and realised that some of the detected lead-based compounds could be used as efficient dryers.
The origin of the detected lead sulphates and phosphates (i.e., whether they were initially present in the ink or they formed during alterations of the ink), remains an open-ended question. Understanding their role in the scribal practices of the ancient Egyptians motivates ongoing research.
Fig. 82: a) Visible light image of a papyrus fragment from Tebtunis. b-c) Macro- and µ-XRF maps showing the distribution of Fe (red) and Pb (blue) in the red hieroglyphic signs that spell out the Egyptian word for star .
PRINCIPAL PUBLICATION AND AUTHORS
New insights into the composition of ancient Egyptian red and black inks on papyri achieved by synchrotron-based microanalysis, T. Christiansen (a), M. Cotte (b,c), W. de Nolf (b), E. Mouro (b), J. Reyes- Herrera (b), S. de Meyer (d,e), F. Vanmeert (d,e), N. Salvadó (f), V. Gonzalez (g), P.E. Lindelof (h), K. Mortensen (h), K. Ryholt (a), K. Janssens (d,e), S. Larsen (i), PNAS 117(45), 27825-2783 (2020); https:/doi.org/10.1073/pnas.2004534117 (a) Department of Cross-Cultural and Regional Studies, University of Copenhagen (Denmark) (b) ESRF
(c) Laboratoire d Archéologie Moléculaire et Structurale, University of Sorbonne, Paris (France) (d) Antwerp X-Ray Analysis, Electrochemistry & Speciation Research Group, Department of Physics, University of Antwerp (Belgium) (e) NanoLab Centre of Excellence, University of Antwerp (Belgium) (f) Departament d Enginyeria Química, Escola Politècnica Superior d Enginyeria de Vilanova i la Geltrú, Barcelona (Spain) (g) Science Department, Rijksmuseum, Amsterdam (The Netherlands) (h) Niels Bohr Institute, University of Copenhagen (Denmark) (i) Department of Chemistry, University of Copenhagen (Denmark)