Multi-analytical characterisation of red colouration on decorated ostrich eggshells from the Middle Bronze Age in Bahrain

In the early 1960s, a Danish archaeological team excavated a group of mounds in Bahrain dating back to 2000 BC. Among their finds were fragments of decorated ostrich eggshells that displayed rectangular engravings as well as red colouring on the outer surface and a uniform red tint on the inner surface. The unpigmented natural coloration of ostrich eggs is the result of adaptations to prevent overheating in the arid habitat, and therefore, the red hue was artificial. The aim of this research was to characterise this coloration. Elemental analysis revealed low iron content, ruling out the use of iron-rich pigments such as ochre, while analysis by molecular spectroscopy could not detect any compounds besides the characteristic constituents of the calcareous eggshell. Thermal experiments on modern eggshells, combined with chiral amino acid analysis, indicated that the red colour on the archaeological samples could have been due to exposure to moderate temperatures. This investigation provides valuable insights into the art and cultural practices of ancient Middle Eastern societies during the Middle Bronze Age, contributing to our knowledge of prehistoric archaeology.