Characterisation of red colour on decorated ostrich eggshells from Bahrain

Gianluca Pastorelli, Mikkel Scharff, Kirsty Penkman, Jørgen Wadum, Jane Richter

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In 1962-63, a Danish archaeological expedition excavated a group of mounds in Bahrain dated to around 2000 B.C. Among other objects, numerous fragments of decorated ostrich eggshells were unearthed. The outer surfaces of these fragments bear engravings in the form of rectangular patterns and some areas coloured in a reddish hue on a white background, while the inner surfaces are uniformly slightly reddish.
Ostrich eggs are naturally glossy, crème-coloured, and are never pigmented. This coloration is the result of an adaptation to the hot, arid ostrich’s habitat, to prevent the eggs from reaching a lethally high internal temperature. Therefore, there is no doubt that the reddish colour on the outer and inner surfaces of the subfossil eggs is artificial.
The aim of this research is the characterisation of the reddish colour. Analyses carried out by SEM-EDX showed an iron content that is too low to be associated with an iron-based pigment such as hematite and is likely due to post-depositional processes. Further analyses by means of ATR-FTIR, micro-Raman and X-ray photoelectron spectroscopies could not detect any compounds/elements besides the characteristic constituents of the calcareous eggshell.
As reported in similar research works [1,2], thermal experiments of fresh ostrich eggshells show that the range of colour found on archaeological samples is caused exclusively by the exposure to high temperature. Since heating ostrich eggshells at high temperatures not only increases the rate of protein degradation, but also enables reactions with higher activation energies to occur, identification of the hypothetical degradation products, for example by high-performance liquid chromatography (HPLC), may act as an indicator of whether a sample has been artificially heated.
This work would allow us to bring a significant contribution to prehistoric archaeology by achieving a new understanding of the art of decorating common objects during the Late Bronze Age.
Original languageEnglish
Publication date2019
Publication statusPublished - 2019
EventTECHNART 2019 - Bruges, Belgium
Duration: 7 May 201910 May 2019


ConferenceTECHNART 2019
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