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Abstracts Frédéric Davidovits Université of Caen, France Pigment "Egyptian blue", used during Antiquity in painting and shaped into blue or green balls, called in latin "caerulea", has been found in Pompei, and Herculanum. The Egyptian blue is a calcium-sodium disilicate of copper, (CaO,Na2O) CuO4SIO2. The text of the Roman architect Vitruvius (7, 11, 1) is the only text which outlines the manufacture stages of this artificial pigment based on silica, copper oxide and alkali. Vitrivius describes the local way of producing it in Verstorius' factory in Puozzoli, near Pompei, during the first century B. C.. Caius Vestorius, a rich banker of Puozzoli, businessman, correspondent of Cicero and Atticus, imported and perfected in Italy the Alexandrine methods of manufacture of the pigment Egyptian blue. One crushes sand (harena) with natron (flos nitri); one obtains a sort of flour and mixes it with copper; this mixture is shaped into a ball, dried in air and fired in earthenware pots. Yet, the scientific analyses of "caerulea" from Pompei and Herculanum show the presence of a high amount of calcium. But Vitruvius's text does not mention any addition of limestone or lime. How was the calcium brought in the mix? The source for the calcium might be the natural "harena" (sand) like the "harena fluviatica" extracted from the river Volturnus in Campania, not far from Pompei, also used for the manufacture of glass (Plin. nat. 36 , 194). It is a silico-calcareous sand. Faventinus (5, p. 308) describes a powder of "harena " (pulvis harenae). An other calcium source is the "flos nitri", which is usually washing soda or natron, and acts as a flux. Pure washing soda does not contain lime. However, Pliny (nat. 31, 114) states that in Egypt, natron is often falsified with some lime, a forgery detected by its taste. It can be assumed that the "flos nitri" described by Vitruvius was imported from Alexandria and contained a fraudulent amount of lime. For the Pompeian "caerulea" produced in Vestorius' factory, during the first century B. C., the source of calcium was the local silico-calcareous sand "harena fluviatica" also used in the local glass industry and/or an imported Egyptian natron adulterated with lime. | Back to Abstracts | Back to the Timetable | |