First evidence for 1st century AD production of Egyptian blue frit in Roman Italy

The considerable amount of research carried out up to present time in an attempt to understand the production technique of Egyptian blue frit is based on analyses of the ancient pigment and its laboratory synthesis. The fortunate finding in Roman Liternum of 1st century AD fragments of ceramic crucibles with adhering remains of a blue pigment allowed laboratory analyses (OM, XRD, SEM–EDS) to be performed on original production debris. The results confirm that the crucibles had been used for the synthesis of Egyptian blue frit and throw new light on the controversial issue of the Roman manufacturing technique of Egyptian blue frit. The results of the analyses indicate that the Egyptian blue frit was produced with a mixture of a local source of silica–lime sand, a fluxer (not identified) and copper scale; the crucibles were also made with local raw materials. The firing of the batch was performed at a relatively low temperature, probably around 850 °C and firing at higher temperatures would have hindered the formation of the cuprorivaite crystals. The analyses suggest that the evaporation of copper during firing of the batch attested in this study is one of the most critical parameters influencing the final blue pigment hue.