L. Beck

Detection limit improvement for Mg in marine foraminiferal calcite by using helium induced X-ray emission

New efforts focus on tools which enable the reconstruction of past climates. For example, the Mg/Ca atomic ratio in marine Foraminifera starts to be used as a proxy for ocean water mass temperature. Because both, Mg content is very low (<1000 ppm) in the calcite shell and samples are difficult to collect, it is necessary to develop non-destructive techniques allowing accurate measurements. We present here a means to improve the detection limit of Mg in thick CaCO3 samples by using helium ions instead of protons to induce X-ray emission. We determine the Mg/Ca concentration ratio of standard CaCO3 powders and Globigerinoides ruber Foraminifera collected in the Equatorial Atlantic Ocean. The results show a decrease in the Mg/Ca ratio with the water depth indicating that the temperature record is partially altered by dissolution processes which should be taken into account in a future calibration model.

Absolute dating of lead carbonates in ancient cosmetics by radiocarbon

Lead carbonate is one of the major compounds of art and archeology used as an ingredient in paint and cosmetics since Antiquity. Accelerator mass spectrometry radiocarbon dating is usually applied to organic remains. Here we extend radiocarbon dating to lead carbonate, an inorganic material. We demonstrate that lead carbonates can be dated. We also show that natural and manufactured make-up powders can be discriminated by radiocarbon. We find that cerussite used for cosmetics was a natural mineral during the Egyptian Kingdom and then a synthesized compound manufactured by the ancient Greeks. Furthermore, we confirm that phosgenite was artificially produced by the Egyptians about 3500 years ago. Our results confirm the expertize of ancient Egyptians and Greeks in the chemical synthesis of cosmetics. The detection of radiocarbon in lead carbonate holds great promise for art history and provides a new tool for the authentication of paintings by dating the lead white pigment.Lead carbonate is found in historical pigments used in paint and cosmetics since antiquity, but radiocarbon dating of inorganic materials is uncommon. Here ancient Egyptian and Greek cosmetics are radiocarbon dated based on their lead carbonate content, allowing synthetic and artificial pigments to be distinguished.