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COMMENTARY
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psimythion and cerussa supply additional details or give variations in the general procedure. Vitruvius,421 in speaking of the manufacture of cerussa at Rhodes, states that a layer of twigs was placed in a large jar, vinegar was poured over the twigs, and pieces of lead were placed on top of them. He also states that the jars were provided with lids to prevent evaporation. Pliny422 gives an outline of two processes: one of them is similar to the process described by Theophrastus, the other is similar to the one given by Vitruvius. Pliny probably obtained his information from these authors. Both Vitruvius and Pliny describe the roasting of white lead to produce red lead, which was also a valuable pigment. Since Theophrastus does not mention this additional step, it seems likely that it was unknown in his day, or at least unknown to him. The most extensive description of the lead corrosion process is given by Dioscorides.423
It is interesting to note that the most satisfactory white lead for use as a pigment at the present time is still the kind produced by the action of acetic acid vapor on metallic lead in the presence of air and carbon dioxide, and much of it is made by the so-called Dutch process. In this method, as in the ancient ones, the lead is corroded in small pots containing dilute acetic acid; the essential difference is that in the modern process the operation is performed on a large scale in a closed building, and an abundant supply of carbon dioxide is furnished by some fermenting material such as spent tanbark.
Specimens of white lead used by the Greeks have been discovered by archaeologists and positively identified by chemical analysis. The most extensive discoveries were made by Shear424 during the excavation of the North Cemetery at Corinth, where small covered bowls in the graves of women and girls were found to contain white lead in the form of pressed cubes, irregular pieces, and loose powder. A representative sample from one of these bowls was examined chemically by Foster425 and found to be lead carbonate. It is interesting that Dioscorides426 mentions
421 VII, 12.
422 XXXIV, 175-76.
423 V, 103 (Wellmann ed., V, 88).
424 Classical Studies Presented to Edward Capps (Princeton, 1936), p. 314.
425 W. Foster, Journal of Chemical Education, XI (1934), 225. 428 V, 103 (Wellmann ed., V, 88).
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