Blackening of the Surfaces of Mesopotamian Clay Tablets Due to Manganese Precipitation

摘要

Blackening was observed on the surfaces of Mesopotamian clay tablets from Umma, Dilbat, Larsa, Ur, Babylon, Uruk, Sippar, and Nippur produced between the Third Dynasty of Ur and the Early Achaemenid Dynasty. Portable X-ray fluorescence analysis revealed that manganese was concentrated on the blackened surfaces. Rod-shaped materials with a length of 100 - 200 nm and a width of 30 nm were observed using a field emission scanning electron microscope. Distinct peaks were not necessarily obtained by micro-X-ray diffractometer analysis, but several samples of the black material showed peaks identifiable as buserite. These results may suggest that blackening on the surfaces of the clay tablets can be ascribed to the activity of manganese-oxidizing microbe. However, the size of the rod-shaped materials is too small compared to common bacteria.