A03_10

Characterization and selection of mortar samples for radiocarbon dating in the framework of MODIS2 intercomparison: results of the Italian laboratories

Maspero F¹, Galli A¹, Panzeri L¹, Martini M¹, Ricci G², Secco M³, Artioli G², Fedi M⁴, Barone S⁴, Liccioli L⁴, Marzaioli F⁵, Passariello I⁵, Terrasi F⁵

¹Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca (Italy) and CUDAM (Centro Universitario Datazioni e Archeometria Milano-Bicocca), Milano, Italy, ²Dipartimento di Geoscienze, Università degli Studi di Padova, Padova, Italy, ³Dipartimento di Beni Culturali, Università degli Studi di Padova, Padova, Italy, ⁴INFN, Sezione di Firenze , Firenze, Italy, ⁵Dipartimento di Matematica e Fisica, Università degli Studi della Campania Luigi Vanvitelli, Napoli, Italy

Since several decades, many efforts have been devoted to improve the accuracy of mortar radiocarbon dating and to assess the reliability of the results in relation with the typology of the examined specimen. Several assumptions for the application of the method are in many cases not fulfilled, among which: a) complete primary limestone dissociation during calcination; b) efficient separation of geogenic carbon contained in calcareous aggregates; c) short carbonation time; d) absence of dissolved CO₂ in running water exchanging carbonate ions. Many laboratories all over the world have proposed different methods to select suitable fractions of mortar particles.

The first intercomparison attempt, involving eight international laboratories, was made in 2016 to reach a common characterization and pretreatment method of mortars to optimize the radiocarbon dating results. Following this first step, a new intercomparison experiment was proposed and set up in 2018 during the Mortar Dating International Meeting (Bordeaux, FR). A new set of three mortar samples was chosen, taking care about the selection of standardized materials (homogeneous, with defined mineral types, devoid of exogenous inclusions, of known ages).

This work describes the results of the Italian laboratories involved in the intercomparison. The samples were characterized, selected and dated depending on each laboratory strategy. The data are encouraging and shed light on future steps to be taken to standardize a method for prior characterization and selection of samples suitable for radiocarbon dating.