Micro‐Raman investigation of terra sigillata slips: a comparative study of central Italian and southern Gaul productions

Abstract

Terra sigillata is certainly the most famous fine ware of the Roman period, and for this reason it has been a subject of interest for both the archeology and archeometry communities. X-ray diffraction studies showed systematic differences in the mineral compositions between central Italian and south Gaul productions. All the slips contain hematite; the Gallic ones embody also a significant content of corundum, while the Italian productions contain a great proportion of spinel. Raman investigation fails to reveal directly these differences because the spectra are dominated by the hematite peaks. However, we originally demonstrate that, due to the occurrence of an upshift of bands, the Raman spectrum of these sigillata slips can be associated with a substituted hematite. This premise has been confirmed by comparing the crystallization of hematite in four annealed clays to that of the ancient slips. The results suggested that the presence of the strong additional Raman band at around 680 cm −1 present in both clays and ancient slips could be associated with the recrystallization of hematite, occurring above 750 • C. It could also be due to the magnetite content, but this hypothesis is not supported by X-ray diffraction data. In addition, the reduction seems to take place only above 1050 • C, as suggested by the unveiling of hercynite as well as the darkening of the clay samples. Raman scattering is shown to be very sensitive to small variations in clays composition and to firing temperature, and it has been successfully used as an in situ sensitive probe for discriminating between Italian and south Gallic productions.

Investigating the firing protocol of Athenian pottery production: A Raman study of replicate and ancient sherds

“…The measured blue-shifts, in both the replicate fired at T1 = 1000°C and the ancient sherd, are comparable to that reported for a 4% increase of Al in the hematite structure. [9,11,14,31] However we must also consider whether other elements found in elevated levels in the gloss relative to the body (notably Mn and Ni, see Fig. 6e), may be contributing to the observed shift.…”

Raman spectroscopy applied to early (ca. 1746–1754) English steatitic porcelains: a tentative study of compositions

“…The peak wavenumber shift and broadening arise from partial Fe/Al substitution and/or Ti substitution. [50,51] The band at 949 cm −1 is the signature of the lead-rich glaze, and the band at 574 cm −1 may indicate the presence of borax in the glaze composition. The Raman spectrum suggests that a higher lead content was used for the red colourant than for the turquoise enamel.…”

Ceramic findings from the archaeological site at Aiano-Torraccia di Chiusi (Siena, Italy): a multi-analytical approach

“…As the spectra of the INGR samples show both maghemite and hematite peaks, it is possible to affirm that the maghemite was not completely transformed into hematite which suggests that the firing temperatures were probably lower than 900°C (Sartoratto et al 2007). This assumption is confirmed by the presence of illite (Leon et al 2010). If heated to 1,200°C It is possible to conclude that the TCC samples were fired at temperatures higher than 900°C: no peaks referring to maghemite phase were evidenced in their Raman spectra and this means the maghemite must have been completely transformed into hematite.…”