Scientific Analysis of Seventh‐century Glass Fragments From the Crypta Balbi in Rome*

Abstract

Inductively coupled plasma emission spectroscopy, reflectance spectroscopy and X‐ray diffraction were used to study seventh‐century AD glass fragments from the Crypta Balbi in Rome. All the samples were found to be silica‐soda‐lime glasses. Iron determines the colour of blue‐green, green and yellow‐green transparent glasses; chemical composition suggests deliberate addition of iron and/or manganese in about half the samples. Copper was found as the main colourant in red, pale blue and blue‐green opaque fragments; elemental copper acts as an opacifier in red glass, and calcium antimonate in white, pale blue and blue‐green glasses. Detection of antimony in transparent fragments suggests recycling of opaque mosaic tesserae.

Colourants and opacifiers in seventh and eighth century glass investigated by spectroscopic techniques

“…3 and Ref. [12]) intense absorption due to Fe(II) ions is the most characteristic feature of samples CB7 and CB15; the different contribution by Fe(II) and Fe(III) ions, as recognisable in the spectra, determines the more bluish hue of fragment CB7 and the more greenish hue of CB15. Samples CB43 and CB46 are intermediate in hue between the first two, but their spectra are different from each other and from those of CB7 and CB15.…”

“…The composition of the studied fragments (21 elements) was obtained previously by inductively coupled plasma optical emission spectroscopy (ICP-OES) and is reported elsewhere [12,13]. All the fragments are soda-lime glass; a particular feature of some of them is a fairly high copper, antimony and/or lead content, irrespective of colour and opacity.…”

“…This paper reports the use of reflectance spectroscopy, X-ray diffraction, and SEM-EDS to study colourants and opacifiers in glass fragments dating from the seventh and eighth century AD. The fragments were excavated in the exedra of the Crypta Balbi in Rome [12,13]. Transparent and translucent glass included fragments of chalices, lamps, window panes, and inlays; they were blue, bluegreen, green, yellow-green, yellow, red-purple or colourless.…”

Los vidrios del rosetón del transepto de la catedral de Tarragona: caracterización, clasificación y alteraciones

“…The colour obtained depends not only of the ions, but also of the presence of other oxides, their state of oxidation and the temperature and conditions in the kiln. Mirti et al (2000) affirmed that the hue is determined by the Fe +2 /Fe +3 ratio, while the saturation depends on the iron concentration.…”

Glass Making in the Greco-Roman World: Results of the ARCHGLASS project

“…This is due to the fact that MnO was often added to the glass as a decolourising agent (Sayre and Smith, 1961;Sayre, 1963;Henderson, 1985;Jackson, 2005;Freestone, 2008;Silvestri, 2008). In analytical studies of Roman glass, MnO is said to have been added deliberately when it occurs at levels above 0.1 -0.2% (Wedepohl et al, 2011a), 0.2% (Sayre, 1963), 0.4% (Brill, 1988), 0.5% (Jackson, 2005) or 1% (Henderson, 1985;Mirti et al, 2000Mirti et al, , 2001. Our results indicate that background levels of MnO, i.e., the amount of MnO coming in with the sand raw material, are even lower.…”