This paper provides a detailed technological characterization of the Roman opus sectile glasses (second century AD) coming from the renowned Gorga collection. Nine glass samples corresponding to imitations of the porfido verde antico, cipollino rosso, rosso antico, giallo antico, diaspro nero e giallo, semesanto and agate/alabaster stones were studied. The aim of this study was twofold: (i) archaeometric, i.e., to provide valuable data on the production, raw materials and techniques of these refined Roman glasses that mimic precious stones and (ii) methodological, i.e., to highlight the good performance of combining polished thin sections and local probe measurements for the study of glassy microstructures. Based on the nature of the flux used, the glasses from the samples were classified as either natron-type or mixed-type (natron/plant ash). The latter stem from remelted glasses and contain relict grains of wollastonite that were not found in the pure natron samples. Relict wollastonite crystals appear to be a proficient petrographic marker to spot recycled glasses along with the commonly used chemical fingerprints. Different production and colouring techniques were identified, even for a given type of imitated stone. Metallic Cu, Ca antimonates and Pb-Fe antimonates were the three opacifiers used for the opaque glasses. Based on the crystal morphologies, metallic Cu and Ca antimoniates were possibly synthesized in situ simultaneously with the glass, whilst the Pb-Fe antimonates were prepared ex situ. The working temperatures for these glasses were estimated within the 900–1100 °C range based on the presence and known thermal stability of some identified crystal phases.

Several scholars and ancient sources highlight the communicative functions of images in the ancient Roman architecture, including plant-based motifs. Among them, Corinthian capitals, usually considered overall a stylistic character, are associated mostly with the Acanthus leaves. Indeed, further neglected plants still need a more precise identification. This paper aims to carry out a systematic analysis of their botanical composition and of the potential encoded symbolic messages. Through an analysis of 83 Roman capitals, overall Corinthian (52), Corinthianising (23), and Composite (8), dated between the II century BCE to the IV century CE from the territory of Rome, we recognised 40 different plant motifs (35 of them identified), resulting in 29 families, 30 genera and 27 species. Their bottom level is characterised by few variations of botanical species, where the recurrence of Acanthu s, representing the idea of Rebirth, is the primary key to the style. The presence of emerging spikelets of Triticum sp., previously unmentioned, seems to have a recurrent and highly relevant augural role of fertility. We cannot neglect some zoomorphic associations, such as the Acanthus leaves that, at distance, show the apotropaic effect of lions’ mouths. The middle level shows the main variability of species, often hosting the presence of Asplenium scolopendrium , having an augural value. The re-flowering flowers motif, with flowers that metamorphose into other plants, recurs in Corinthianising and Composite typologies, suggesting a never-ending life. The apical level, through the abacus plants and snakes, primarily conveys the ideas of strength, light, and salvation. Graphic abstract