Evolution of terra sigillata technology from Italy to Gaul through a multi-technique approach

Abstract

International audienceTo understand how the terra sigillata technology was transferred from Italy to Gaul, a large corpus of samples from various worskshop was studied by standard laboratory techniques (Raman spectroscopy, SEM, electron microprobe and colorimetry). Based on these results, a few representative samples were selected and investigated by synchrotron radiation at ALS on the 12.3.2 microdiffraction beamline. The beamline is very adapted to the crystallographic study of thin layers and allows us to determine precisely the mineral composition of the sigillata slips. The set of findings revealed significant differences between the Italic and Gallic slips, which suggest a modification in the manufacturing process. The transfer of the sigillata technique in Gaul is associated to an increase of the firing temperatures due to the use of more refractory clay. This change has no significant influence on their esthetic appearance (brilliance and color) but modify their mechanical properties, resulting in a stronger resistance for the Gallic slips. The implication of these results in archeological context is discussed. In particular, we will try to propose assumptions on the reason of the change in the manufacturing process

Nano-crystallization in Decorative Layers of Greek and Roman Ceramics

“…This results in a slight increase of the average size of hematite crystals (30 → 50 nm), but this effect is balanced both by the lower crystal density (Fe rate is lower in Gallic Terra Sigillata) and a higher Al substitution (around 8-9 % in Gallic Terra Sigillata). Recent studies showed that the rate of substitution increases with the temperature and that the rate value was higher in Gallic productions than in Italic ones (Leon et al 2010(Leon et al , 2015. One consequence is that the two types of production present similar colours.…”

“…In some cases, the discrimination can be finer and allows for separating the production of an individual pottery-making firm inside the same workshop. For example at Arezzo, the products of "Ateius" can be separated from the one of "Perrenius" on the basis of their element compositions (Leon et al 2015). Of course, it is also the case for other ceramic types.…”

“…The attic and Campanian ceramics were provided by the laboratoire d'Archéologie des Sociétés Méditerranéennes and come from the Lattes and Narbonne excavations respectively. The terra sigillata data were extracted from Leon's work (Leon et al 2015) as one can observe comparing the elemental compositions of two main italic workshops (Arezzo, Pisa) of Terra Sigillata and the one (La Graufesenque) of the main southern Gallic workshops. In some cases, the discrimination can be finer and allows for separating the production of an individual pottery-making firm inside the same workshop.…”

Natural Nanosized Raw Materials and Sol-Gel Technology: The Base of Pottery Since Millenniums

“…The size reduction of particles to nanorange modifies the shape of electronic absorption bands and hence modifies the electronic gap, leading to a small colour change. This phenomenon is at the origin of Roman Sigillatta's (Leon et al 2015) nice colours where the orange to red colour of the fired slip arise from the association of micronic haematite and/or hercynite grains. Rather similar fine microstructure are observed for Iznik red (Armenian bole) (Colomban et al 2004;Simsek and Gecckinli 2012), red Meissen décor (Colomban and Milande 2006) and French faience red décor obtained using Thiviers sandstone as red pigment precursor.…”

“…Mass production was experimented very early: Roman potters produced sigillata (Leon et al 2015), and Roman glassmakers glass ingots, in very limited places that can be considered as the first manufactures. Ingots were exported to many places where glassformers elaborated artefacts (Fontaine and Foy 2007).…”