Mortar Dating Methodology: Assessing Recurrent Issues and Needs for Further Research

Abstract

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. To evaluate various sample preparation methods for radiocarbon (14C) dating of mortars as well as to compare different dating methods, i.e. 14C and optically stimulated luminescence (OSL), a mortar dating intercomparison study (MODIS) was set up, exploring existing limits and needs for further research. Four mortar samples were selected and distributed among the participating laboratories: one of which was expected not to present any problem related to the sample preparation methodologies for anthropogenic lime extraction, whereas all others addressed specific known sample preparation issues. Data obtained from the various mortar dating approaches are evaluated relative to the historical framework of the mortar samples and any deviation observed is contextualized to the composition and specific mineralogy of the sampled material.

Absolute dating of lead carbonates in ancient cosmetics by radiocarbon

“…They are formed during the drying up of salt lakes in summer. Sodium carbonates can be formed at the surface by absorption of carbon dioxide from the atmosphere or in the brine by combination of HCO 3 2− with Na 35 . Over the years the lake builds up a stratigraphy of deposits which are complicated by partial dissolution during the winter when the water rises again.…”

“…As early as the 1960s, 14 C dating was extended to building materials 1 . In particular, mortar which incorporates atmospheric carbon dioxide as it hardens, has been extensively studied and used to date churches and Roman buildings 2,3 .…”

The State-of-the-Art of Dating Techniques Applied to Ancient Mortars and Binders: A Review

“…Previous studies have shown that a thorough mineralogical, petrological and geochemical characterization of the mortar sample is advised in order to plan a better sample preparation and dating strategy, or at least to have a basis for the correct interpretation of the results (Addis et al 2016(Addis et al , 2019Van Strydonck 2016;Marzaioli et al 2019). Hayen et al (2017) even stated that "Prescreening and characterization of the mortars should become a standard approach prior to the mortar dating in order to understand the failure risks of the dating process and to evaluate the data obtained".…”

PRETREATMENT PROTOCOLS PERFORMED AT THE ROYAL INSTITUTE FOR CULTURAL HERITAGE (RICH) PRIOR TO AMS 14C MEASUREMENTS

“…For mortars and lime burials, the CO 2 fractions are obtained by the titration method or sequential dissolution (Van Strydonck et al 1982Hayen et al 2017). The powdered mortar sample is kept in suspension while 2 mL of 0.1 M HCl are added for the first four fractions then different amounts of~2.2 M HCl are added for the remaining fractions.…”