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Evidence for Multiple Firings of Athenian Pottery Karen Trentelman, The Getty Conservation Institution, DMR 1041808

Athenian black-figure and red-figure pottery has long been thought to be produced in a single firing by cycling the pottery through oxidative and reductive cycles which created the distinctive orange and black appearance of the vessels. However, our research has uncovered new evidence indicating the use of multiple firings. For example, in the red figure ceramic from the 5th c B.C. (JPGM 95.AE.31.2) shown here the black fine lines that delineate the hand (called relief lines) and the broad washes used to create the background were found to have different microstructures, indicating they were applied to the ceramic sequentially with separate firings in the kiln to build up the design in stages.

Using scanning transmission electron microscopy (STEM), detailed images of the microstructure were obtained which revealed information on the melting behavior of the ceramic materials. Compared to the background (C), the relief line (D) appears more melted, indicating it was subjected either to a hotter temperature or the same temperature as the background but for a longer period of time. The relative differences in the vitrification of the background and relief line provide material evidence that this sherd must have been fired at least twice.

A and B: 5th C. BC red-figure ceramic fragment attributed to the Kleophrades painter and detail showing relief line and background decoration. C : STEM image of background gloss. D: STEM image of relief line showing a distinctive microstructure caused by a different firing environment.

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Journal of the American Ceramic Society 96(7), 2031-2035.

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Is Zn a marker of clay processing?Karen Trentelman, The Getty Conservation Institution, DMR 1041808

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Zn content from 19 sherds. Analysis of the body and the gloss show different distributions of Zn. The elevated but variable levels of Zn in the gloss were likely introduced during the processing of clay.

Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) provides information on the trace element content of the ceramics that can be used to establish the geological provenance of the raw materials or point to anthropogenic markers indicating how these ceramics were produced.

Results from the study of 19 sherds from red and black figure vessels showed that the body ceramic and the black gloss material share many compositional characteristics, suggesting that they are derived from similar geological sources. However, as shown in the bottom figure, notably higher Zn levels were found in most of the gloss samples than in their corresponding body ceramics. Based on the abnormally high Zn content of the gloss clay (~500-2000 ppm) it is speculated that this clay slip was either derived from sources near ancient mines rich in minerals containing Zn (e.g., Laurion, Greece) or that the clay was treated during refinement with acid mine run-off water, which is often rich in this trace metal.

Ancient treatises (Pliny the Elder) discuss acid mine run-off water to make vitriol (sulfuric acid). We postulate that the clay from which the gloss slip was derived could have been treated with this acid to remove CaCO3 that, if present, could prevent the vitrification of the gloss material. This may also have had the unintended consequence of increasing the Zn content, but which may serve as a marker of this activity.

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Lab manager David Carson (left) and Co-Pi Marc Walton (right) running the Getty Conservation Institute’s LA-ICPMS (GCB Optimass 9500).