A06_P02

When corrosion is useful: the incorporation of ¹⁴C in lead white

Beck L¹,  Messager C¹, Germain T¹, Hain S¹

¹LMC14-ARTEMIS, Gif-sur-yvette, France

Recent studies have shown that radiocarbon dating can be applied to inorganic compounds such as synthetic lead carbonates, cerussite (PbCO₃) and hydrocerussite (2PbCO₃Pb (OH)₂ (Beck et al. 2019; Messager et al. 2020) . Known as lead white, lead carbonates were used as white pigment or cosmetics from the 4th century BC to the 20th century and were formed by the corrosion of metallic lead by vinegar and horse manure up to the 19th c. In order to better understand the incorporation of ¹⁴C in cerussite and hydrocerussite, lead carbonates were produced in laboratory by the corrosion process under various monitored experimental conditions. Lead carbonates were obtained using two types of acid (vinegar containing ¹⁴C vs ¹⁴C free acetic acid) and three types of CO₂ sources (air, horse manure containing ¹⁴C and ¹⁴C free fossil CO2 gas). Twelve different conditions were tested and ¹⁴C was measured in all the corrosion products: lead acetates when CO₂ was absent and cerussite when CO₂ was present. The results show that cerussites carry the ¹⁴C signature of CO₂ produced by the horse manure or from the fossil gas, indicating that vinegar/acetic acid acts as a precursor and horse manure as a reagent to produce carbonates. These experiments demonstrate that CO₂ produced by horse manure fermentation is incorporated into the corrosion products, meaning that the carbonate function of the lead carbonates carries a ¹⁴C signature corresponding to the natural organic matter. This step is crucial for an absolute dating of lead carbonates by the radiocarbon method.