Absolute Dating of Mortars – Integrating chemical and physical techniques to characterize and select the mortar samples

International audience; Absolute dating of mortars is crucial when trying to pin down construction phases of archaeological sites and historic stone buildings to a certain point in time or to confirm, but possibly also challenge existing chronologies. It should become a standard tool for archaeometric research as it contributes considerably to the historical, artistic, social, cultural and touristic valorisation of our built heritage. To compare on the one hand the different methods – radiocarbon and OSL – as well as to evaluate the best method of how to prepare samples for radiocarbon dating, an intercomparison study amongst various laboratories was set up. The results of radiocarbon dating of mortars depend very much on the accuracy with which minute differences in crystal structure between the various sources of anthropogenic and geogenic carbonates can be discriminated. As a detailed characterisation of the samples prior to the actual dating was necessary, the laboratories cooperated and employed a range of methods.