Glass in imitation of exotic marbles : an analytical investigation of 2nd century AD Roman sectilia from the Gorga collection

The materials uncovered in excavations in several provinces of the Roman empire provide important evidence to the frequent use of glass in most precious opera sectilia. Glass pieces imitating a dozen of ancient marbles and exotic stones have been identified in the collection belonged to Evangelista Gorga, samples of which were selected for analysis in order to obtain valuable information on the Roman glassmaking technology of the 2nd century AD, especially on coloration techniques. The monochrome and polychrome glass tesserae replicating precious marbles and rare stones were: porfido verde antico, litomarga verde, turquoise, pavonazzetto, gabbro eufotide, diaspro nero e giallo, semesanto, alabastro tartarugato, rosso antico, cipollino rosso, giallo antico, and onyx. XRF quantitative chemical composition was determined allowing the types of glass used and the colouring techniques to be identified. Results have been compared with similar data obtained by studies on coloured Roman glass and mosaic tesserae. Similarities and discrepancies are discussed and hypotheses are suggested on the technology of this extraordinary Roman production.