The Technology of Copper-Based Red Glass Sectilia from the 2nd Century AD Lucius Verus Villa in Rome

Abstract

This work aimed to investigate the origin of different red hues of Roman copper-based red opaque glass sectilia, to shed light on the production technology behind them. This objective was achieved by the depth study of the samples of glass sectilia, which decorated the villa of co-Emperor Lucius Verus (161–169 AD). These were selected for analysis due to their abundance, the certainty of their date and of their different red and orange hues. Using OM (optical microscopy), colourimetry and FORS (fibre optical reflectance spectroscopy) spectroscopy, four red and four orange hues were individuated. A set of representative samples for each hue was analysed by EPMA (electron probe microanalyses) to detect any correlation between colour and chemical composition. Crystalline phases were investigated through high-resolution FEG–SEM (field emission gun scanning electron microscope), μRaman spectroscopy and XRD, for the identification of colouring and opacifying agents and to understand how the different hues are affected by their shape, concentration and dimension. Sub-micrometric particles of metallic copper and cuprite crystals were identified as both the colouring and opacifying agents. These were not present in the same samples and were manufactured by two distinct colouring techniques, corresponding to two different glass chemical compositions. The size and the number of the colouring particles were the main factors that distinguished one hue from another. Although produced through different colouring techniques, some red samples appeared to be very similar to each other. These data enrich a period of the Roman age through some analyses and allow the identification of the type, as well as some of the production conditions of opaque red glass produced during 2nd century AD, which could be considered to be a period of transition from one technology to another.

Multi‐technique characterization of glass mosaic tesserae from Villa di Teodorico in Galeata (Italy)

“…The red color of R1, R2, and R3 is due to metallic copper Cu 0 , present as suspension of submicrometer colloidal particles, as FORS (inflection point between 590 and 595 nm) [ 11 ] and XRPD demonstrated (Figure 4a,b). Furthermore, SEM‐EDS proved that copper levels of R2 (CuO 9.8 wt%) are higher than R1 (CuO 1.5 wt%) and R3 (CuO 3.6 wt%).…”

“…In the orange tile O1, FORS analyses (Figure 5a), XRPD (Figure 5b), and mainly micro‐Raman spectroscopy (Figure 5c) identified cuprite (Cu 2 O), [ 11 ] which acts as colorant and co‐opacifier together with cassiterite (SnO 2 ). [ 18 ] FORS spectrum shows points of flex at 490/595/685 nm, ascribable to cuprite (Figure 5a).…”

“…[18] FORS spectrum shows points of flex at 490/595/685 nm, ascribable to cuprite (Figure 5a). The Raman spectrum [4,5,11] of crystalline inclusions (Figure 5d) shows the vibrational features of cuprite with the main peak at 220 cm À1 , in addition to characteristic peaks of cassiterite (Figure 5c). The formation of Cu 2 O needs reducing atmosphere in the furnace and high content of copper and lead, [5,18] as it is demonstrated by SEM-EDS.…”

“…Raman microspectroscopy is suitable as a main technique in this complex analysis, being able to obtain information on both crystalline and amorphous materials, on the bulk and on the micrometric inclusions, even embedded in the glass, without necessity of preparation of the samples. This work reports the results of an archaeometric investigation performed on different glass mosaic tesserae by using an analytical approach that included micro-Raman spectroscopy, [4][5][6] field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), [7,8] X-ray powder diffraction (XRPD), [9] UV-visible-NIR diffuse reflectance spectrophotometry with optic fibers (FORS) [10,11] and optical stereo-microscopy. The detected coloring and opacifying agents were compared with those found on contemporary and previous mosaic tiles coming from the same geographical area.…”

Aqua Traiana, a Roman Infrastructure Embedded in the Present: The Mineralogical Perspective

“…Important information can be obtained by the analysis of the materials these societies produced. In this perspective, archaeometry has recently paid increasing attention to the mineralogical and chemical study of geomaterials [1][2][3][4][5][6][7][8][9][10] to reconstruct technological knowledge and skills acquired by ancient populations.…”