HOW THE INCORPORATION OF 14C IN LEAD WHITE MAKES ITS ABSOLUTE DATING POSSIBLE

Abstract

ABSTRACT Known as lead white, lead carbonates were used as white pigment or cosmetics from the 4th century BC to the 20th century AD. Lead white was produced by the corrosion of metallic lead by vinegar and horse manure up to the 19th c. In order to document the incorporation of carbon in the corrosion mechanism, lead carbonates were produced in the laboratory under monitored experimental conditions using materials with different isotope signatures in 14C and 13C. Six experimental setups were defined combining vinegar, acetic acid, horse manure and fossil CO2 gas. The corrosion products were characterized by X-ray diffraction. 14C content and δ13C values of the initial reactants and the final products were measured by accelerator and isotopic ratio mass spectrometry (AMS and IRSM). The reaction between lead and vinegar or acetic acid resulted in lead acetates with a carbon isotopic signature close to that of the corrosive reagent. In the presence of CO2, the carbonatation reaction occurred and the cerussite produced had a predominant 14C signature of the carbon dioxide source. These experiments demonstrate that the CO2 produced by horse manure fermentation is incorporated into the corrosion products, allowing the absolute dating of lead white by the radiocarbon method.