Black–Appearing Roman Glass

Abstract

In this chapter we discuss the possibility of using small segments of the whole glass production of a certain age to elucidate the global chronology and the geographical origin of glass in the period of interest. In particular, deeply coloured and black-appearing glass dating to the Roman Age (first century BC-fifth century AD) has been quantitatively analysed in order to extract information that can help our understanding of the organization of glassmaking, trade and glassworking in that era.A large number of archaeological glass fragments from the western and eastern parts of the Roman Empire has been gathered and analyzed by means of scanning electron microscope-energy-dispersive X-ray spectroscopy (SEM-EDX) and laser ablation-inductively-coupled plasma-mass spectrometry (LA-ICP-MS).The glass samples analysed are macroscopically black, however, when the glass is examined in thin layers, a distinction appears between actual black glass (no hue perceived) and deeply coloured glass (a dark brown/purple/green tint can be seen). Background Roman Glassmaking and Glass MarketGlassblowing, introduced halfway through the first century BC, contributed to turning glass from an expensive material into an affordable commodity. As a consequence the glass market expanded and large amounts of glass were produced in order to satisfy the needs of consumers in Rome and its provinces. In this context it is interesting to explore the dynamics of the two different steps of glass production, namely glassmaking and glassworking.

An Archaeometric Analysis of Black-Appearing Iron Age Glass Beads from Vinha das Caliças 4 (Portugal)

“…The relationship between colourant concentration, glass thickness and transparency, as well as the lighting under which glass is observed can be summarized by Lambert-Beer Law: I = I 0 exp(−εcd); where I = transmitted intensity at a considered wavelength, I 0 = the incident intensity at a considered wavelength, d = the thickness of the sample, c = the concentration of the colouring agent, and ε = the absorption coefficient [54]. In reality, hues of black-appearing glass are often reported as green, blue, purple, or brown when samples are observed under transmitted light or as thin layers [55][56][57], which can sometimes hinder the identification of black-appearing glass in the literature. However, even in the case of "black" glass, i.e., glass of non-perceivable hue, the colouring species are the same as those recorded for black-appearing/deeply coloured glass [55].…”

“…During the Roman Imperial period, black-appearing glass was being produced on a large scale, with production technology changing through time and according to consumer demands. Four major groups of black Roman Imperial glass (1st-5th c. AD) defined on a large dataset from European and Mediterranean sites include (naturally) Fe-coloured plant-ash glass, Mn-coloured purple/black natron glass, Fe-coloured black natron glass, and an Fe-coloured black HIMT-like glass [56,57,63,64].…”

“…The relationship between Ba, Pb, and Zn in Group 4 could, for instance, be indicative of the addition of lead slags to the glass. Lead slags are known to contain iron, barium, and zinc [57], and are usually associated with silver extraction [41,[107][108][109]. Their use has been documented in the production of medieval lead glass [107,109,110], including high-Ba Umayyad (mid-8th c. CE-818 CE) lead glass from Šaqunda (Cordoba, Spain) which was linked to the use of lead slags from silver-mining operations at Villanueva del Duque mines (Spain) by Pb isotope analysis [107].…”