Documenting the history
of technology

But, this was to ignore the practices of the ancient craftsmen whose know-how involved ingredients of organic origin in the production of materials! Carbon 14 from charcoal is therefore found trapped in ancient irons and enables their period of production to be identified [2][2] DOI: 10.1017/RDC.2016.109.

After developing the dating of ferrous alloys in collaboration with the Archaeomaterials and Alteration Prediction Laboratory (LAPA), the Carbon 14 Measurement Laboratory (LMC14) [3][3] Plateforme nationale CEA/CNRS/IRD/IRSN/ministère de la Culture, UMR 8212 continues to innovate and carried out the very first dating of lead carbonates. These compounds are extensively present in our cultural heritage. In art and architecture, they are the components of the white paint used by European artists from the Greek period until the beginning of the 20^th century. In archaeology, their presence in Antiquity and 18^th century cosmetics indicate their use in the home. Lead carbonates exist naturally, but those used in paints or cosmetics were synthetic. The pigment or white powder was then called Venetian ceruse or lead white.

Our first evidence of the synthesis of lead white is described in a 4^th century BC recipe by a Greek author, Theophrastus. To prepare lead white, fine slivers of lead metal are placed in contact with vinegar vapour in a fermenting environment (horse manure, wine lees, tannin, etc.). These are organic ingredients that will “mark” the lead white with carbon 14. The incorporation of the radioactive isotope into the pigment will then act as a chronometer.

Greek and Egyptian cosmetics were thus for the first time dated successfully in 2018 [4][4] www.nature.com/articles/s42004-018-0034-y [5][5] www.pourlascience.fr/sd/archeologie/datation-au-carbone-14-un-nouvel-outil-pour-etudier-lorigine-des-cosmetiques-antiques-14405.php. Carbon 14 dating confirmed the first chemical synthesis of phosgenite, a lead carbonate that is rare in nature (formula Pb₂Cl₂CO₃), carried out in Egypt about 3,500 years ago. A pink blush consisting of lead white and discovered in the tomb of a young girl in Greece was also investigated. Dating of this cheek powder demonstrated that it was indeed synthesised between the 4^th and 3^rd centuries BC, using the process described in the recipe reported by Theophrastus. For phosgenite, the method of manufacture was revealed by a later recipe from Dioscorides, a Greek doctor and botanist from the 1^st century AD [6][6] Walter et al, 1999. Making make-up in Ancient Egypt. Nature. 397:483-484. In both cases, carbon 14 was trapped but its source is not clearly identified in these recipes. It was not until the end of the 13^th century that horse manure was clearly mentioned, thus providing a direct indication of a carbon dioxide atmosphere used to manufacture lead white!

This pigment was to last until the 20^th century, when it was finally replaced owing to its toxicity. Dating lead white is thus a means of authenticating paintings more than two thousand years into the past: the potential repercussions for the art world are considerable! A thesis on this subject is currently in progress at LMC14. n