Calcareous nannofossil assemblage in paintings chalk ground for provenance analysis: three original paintings compared to european source materials

Abstract

Chalk has been used since Antiquity for various purposes, and since Gothic for preparatory layers of painted cultural heritage objects. Several materials are called chalk in Cultural Heritage, but this work especially focuses on chalk composed of calcareous nannofossils (up to 98%). These are fossil remains of photoautotrophic algae generally smaller than 30 μm. They are mainly visible as platelets of various shapes under a cross-polarised or scanning electron microscope. The provenance of chalk can be determined using calcareous nannofossils due to their well-known paleobiogeographic localities. They are already used as proxies since the 90s in Cultural Heritage, but rarely for paintings. In this work, 6 chalk historical mining areas were chosen: Germany (Ruegen), France (Champagne, Meudon), Belgium (Mons), England (Norfolk) and Italy (Bologna). Natural and processed chalk were used as reference materials and compared to 3 original paintings. The difference between the chalks calcareous nannofossil assemblages was shown using multivariate statistical analysis based on species relative abundance. Marker nannofossil species were defined for each chalk locality. One painting material could not be originated due to the preservation of its nannofossils assemblage, but the origins of the rock chalk material from the two other paintings could be geographically located in France.