Blue shade hues: a study of blue pigments used byudRomano-British wall-painters

摘要

Following an earlier study of different coloured pigments used in Roman wall-plaster paintings, this research project investigates the use of the synthetic pigment commonlyudknown as Egyptian Blue in Romano-British wall-plaster paintings. Samples of Egyptian Blue pellets were obtained from excavations at the Romano-British sites of FishbourneudRoman Palace, near Chichester, Piddington near Northampton, Turners Hall Farm, near St Albans, and from excavations at Verulamium (Roman St Albans).ududThe aim of this study is to determine the chemical composition, fabric and texture of each pellet as well as attempting a textural and geochemical classification of the pellets, using well established analytical techniques, particularly LA-ICP-MS and SEM-EDAX. The colour of the pellets was examined and identified using the Munsell Book of Color (Matte Finish Collection) 1973. The results of the analysis of the Egyptian Blue pellets found on Romano-British sites showed that differing amounts of silica, copper, calcium, as well as smaller amounts of other elements, were used in their manufacture. Most of the pellets examined appear to have been manufactured locally, though some were almost certainly imported.ududExperimental work was undertaken, both in the laboratory and out in-the-field where a reconstructed Bronze Age Clamp Kiln and an Iron Age Belgic Kiln were used, to reproduce the synthetic pigment Egyptian Blue, using a recipe similar to that used by earlier investigators. Such recently manufactured Egyptian Blue pellets were applied, as audpigment, to damp lime mortar, in an attempt to correlate the achieved colour with the firing time.ududSimilar techniques were used in an attempt to ascertain the nature of the pigments used on the small fragments of painted wall-plaster found in a back filled trench, from Wheeler’s 1930 - 33 excavations at Verulamium. On two of the fragments gas chromatographic analysis was applied to determine the nature of the binding material that might have been used.ududThis study is thought to be the first in-depth investigation of Romano-British Egyptian Blue pellets and thereby contributes to the art history and archaeological knowledge of this period.