The palaeo-Christian glass mosaic of St. Prosdocimus (Padova, Italy): archaeometric characterisation of tesserae with antimony- or phosphorus-based opacifiers

Silvestri, Alberta; Tonietto, Serena; Molin, Gianmario; Guerriero, P.

doi:10.1016/j.jas.2012.03.012

Cited by 43 publications

(31 citation statements)

References 37 publications

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“…In fact, tesserae from churches in Rome (from the 4 th to the 12 th c. [26,[81][82][83][84]) and from Southern Italy (Piazza Armerina, 4 th c. [84]; Foggia and Faragola, 6 th c. [86,87] show the persistence of a Roman technology (natron base glass with calcium antimonate as opacifier). Tesserae from Ravenna [38,61,88], Vicenza and Padova [40] reveal two different supplies during the 5 th century that could be linked to two workshops. The first one produced tesserae with one technique attested in Rome and in southern Italy (natron glass with calcium antimonate); the second producing tesserae with another technique (natron glass with calcium phosphate), as documented in Eastern Mediterranean workshops [15,[34][35][36][37].…”

Section: Resultsmentioning

confidence: 99%

“…These opacifiers remained in the use until the Renaissance and even modern times. Calcium phosphate was also used as opacifier from the 5 th c. onwards, especially in the Eastern Mediterranean [34][35][36][37][38][39][40]. From the 10 th c. onwards, Byzantine glassmakers produced mosaic tesserae employing quartz (ground silica sand), a less efficient but extremely cheap opacifier [41][42][43].…”

Section: Introductionmentioning

confidence: 99%

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Late Roman and Byzantine mosaic opaque “glass-ceramics” tesserae (5th-9th century)

Neri

Morvan

Colomban

et al. 2016

Ceramics International

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Forty-two mosaic coloured/opaque "glass" tesserae from three sites (Milan, Italy; Durrës, Albania; Hierapolis, Turkey) situated in the Western and Eastern parts of the Roman/Byzantine Empire, dated between the 5 th and the 9 th centuries, were studied by optical microscopy, SEM-EDX and Raman microspectroscopy in order to investigate the nature of their pigments and opacifiers as well as the microstructure of glass ceramic materials. The Raman signatures of glass matrix and phases dispersed in the soda-lime glassy matrix showed the presence of six opacifiers/pigments. The use of soda ash glass in the tesserae from Durrës (post 8 th c.) allows refining the mosaic debated chronology. The use of soda ash matrix glass together with the presence of calcium antimonates (Ca 2 Sb 2 O 7 and CaSb 2 O 6 ), pyrochlore solid solution/Naples' yellow (PbSb 2-x-y Sn x M y O 7-δ ) and cuprite (Cu 2 O) or metallic copper (Cu°) in many samples show the technological continuity in a Roman tradition. However, the presence of cassiterite (SnO 2 ) and quartz (SiO 2 ) in one sample from the beginning of the 5 th century, diverging from Roman technology, offers a chronological marker to identify newly (not re-used) produced tesserae. Graphical abstract HighlightsOpaque/coloured glass mosaic tesserae exhibit a glass ceramics microstructure.The innovative use of cassiterite (SnO 2 ) and quartz (SiO 2 ) in 5 th century tesserae is evidenced.The technological innovations went alongside the continual use of Roman recipes (calcium antimonate and yellow pigments). NoveltyThe first use of cassiterite and quartz in the beginning of the 5 th c. as well as the use of calcium antimonates after Roman times in the tesserae produced ex novo with mixed glasses were demonstrated.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Late Roman and Byzantine mosaic opaque “glass-ceramics” tesserae (5th-9th century)

Neri

Morvan

Colomban

et al. 2016

Ceramics International

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“…Groups 2 and 3 are thought to come from the Erzgebirge in Central Europe. This classification has been used in a limited way (Genga et al 2008;Silvestri et al 2012) and is applied here more systematically in this paper.…”

Section: The Establishment Of a Databasementioning

confidence: 99%

Tesserae Recycling in the Production of Medieval Blue Window Glass

Bidegaray

Pollard

2018

Archaeometry

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The purpose of this paper is to develop a means of quantifying glass recycling and to discuss the ‘anachronistic’ chemical composition of medieval blue window glass. This method relies on a new numerical method using kernel density estimates and is based on a database of published glass chemical compositions. It seeks to reveal when, to what extent and why blue tesserae were recycled for the production of French and English blue glass. First, it is suggested that blue glass had an ‘anachronistic’ chemical composition only before the 13th century. Second, the ‘anachronistic’ chemical composition of 12th‐century blue glass comes from the recycling of both blue tesserae and non‐coloured glass. Finally, this recycling was motivated by the scarcity of cobalt sources until mines were found in the 13th century.

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“…In the present assemblage, given the high tin detected in the opacifiers of some tesserae analyzed here, the most likely hypotheses are the use of tin-rich metallurgical scraps as the source of lead or the intentional addition of it as a stabilizer [17]; it is unlikely that this element is a pollutant s.s. The occasional presence of iron in the crystals, which was already detected in Roman and Byzantine yellow glasses [9,17,18], is also of unclear origin, and pollution or a deliberate addition [17] are both reliable hypotheses. In addition, as can be observed in Figure 10, the collapse of the peak at about 200 cm −1 , the strengthening of the band at 330 cm −1 and the broadening of that at 510 cm −1 suggest firing temperatures of about 900-1000 • C for the production of Pb-antimonate [55].…”

Section: Yellow and Green Tesseraementioning

confidence: 94%

“…and Byzantine yellow glasses [9,17,18], is also of unclear origin, and pollution or a deliberate addition [17] are both reliable hypotheses. In addition, as can be observed in Figure 10, the collapse of the peak at about 200 cm −1 , the strengthening of the band at 330 cm −1 and the broadening of that at 510 cm −1 suggest firing temperatures of about 900-1000 °C for the production of Pb-antimonate [55].…”

Section: Yellow and Green Tesseraementioning

confidence: 99%

A Mosaic of Colors: Investigating Production Technologies of Roman Glass Tesserae from Northeastern Italy

Maltoni

Silvestri

2018

Minerals

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In the current study, a set of 60 glass tesserae from two disrupted Roman mosaics located in Pordenone and Trento (northeastern Italy) are analyzed, with the aim of investigating the coloring and opacification techniques, with a focus on the causes of specific textural features. All the available colors and textures were selected for archaeometric analyses, in order to guarantee the full characterization of both assemblages and comparisons between the two sites. The applied analytical protocol comprises micro-textural and preliminary chemical characterizations of the tesserae by means of OM and SEM-EDS, mineralogical analysis of the opacifiers by XRD and chemical analysis of the glassy matrices by EPMA; in addition, on specific tesserae, micro-Raman spectroscopy, FORS, and EPR were also performed to clarify the type of opacifer, coloring ion and oxidation state, respectively. Results show that both the base-glass and the coloring/opacification techniques identified are consistent with the presumed Roman dating of the mosaics. All the tesserae are natron-based and chemically comparable with major Roman compositional groups, except for red samples. Antimony-based opacifiers are identified in most of the blue, turquoise, white, yellow and green tesserae, and copper-based opacifiers in the red ones; cobalt and copper are the most frequent ionic colorants used to obtain various shades of blue, turquoise and green colors. Despite the general comparability of both assemblages with the published data on glass tesserae coeval in age, the present study shows differences in the technological solutions used for obtaining the same color, and less common coloring and opacification techniques in three samples from Pordenone. The banded textures of some tesserae were also carefully investigated, and multiple factors influencing the changes in color (different distribution or relative abundance of opacifiers, crystal size, micro-texture, chemical composition of glassy matrix) are identified.

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The palaeo-Christian glass mosaic of St. Prosdocimus (Padova, Italy): archaeometric characterisation of tesserae with antimony- or phosphorus-based opacifiers

Cited by 43 publications

References 37 publications

Late Roman and Byzantine mosaic opaque “glass-ceramics” tesserae (5th-9th century)

Late Roman and Byzantine mosaic opaque “glass-ceramics” tesserae (5th-9th century)

Tesserae Recycling in the Production of Medieval Blue Window Glass

A Mosaic of Colors: Investigating Production Technologies of Roman Glass Tesserae from Northeastern Italy

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