Determining the use of ancient ceramic artefacts through combined morphological and magnetic analyses: the case of Villa del Foro, Northern Italy

Abstract

Even though multidisciplinary approaches are widely used for the investigation of archaeological findings, magnetic analyses are still little exploited and only rarely applied to the determination of ancient artefacts use. Here, we present the results of a combined archaeological, morphological and 2 magnetic study carried out on the ring-shape clay artefacts found in large quantities at the protohistoric site of Villa del Foro (Alessandria, Northern Italy). The shape and significant number of such artefacts make their archaeometric investigation very interesting to understand the technological conditions of their production and use. A morphological investigation carried out on 640 fragments showed inhomogeneity in their dimensions, colour, form, and clay refinement.Magnetic measurements show thermal stability after heat treatment up to around 500-600 o C, while further heating at higher temperature introduces some magnetic mineralogy changes. Thermal demagnetization of the samples generally shows a strong and stable thermal remanent magnetization.In few cases, a clear secondary component is present, suggesting partial re-heating or displacement at temperatures ranging from 200 o C to 450 o C. The results obtained indicate that the investigated ring-shaped artefacts were baked during their manufacture at temperatures of at least 600 °C. The archaeomagnetic investigation does not show any systematic evidence for magnetic components related to cooking activities and it is therefore suggested that the rings were used as weight looms and baked only during their production procedures. Such pilot study can be used as reference for the identification and study of similar objects found in other archaeological sites worldwide.

Applying thermal demagnetization to archaeological materials: A tool for detecting burnt clay and estimating its firing temperature

“…This method has been used to reconstruct site formation processes of structures destroyed by conflagration [ 25 – 27 ]. Thermal demagnetization has also been used in order to examine the stability of the natural remanent magnetization (NRM) [ 18 , 21 , 22 ]. The use of thermal demagnetization for the reconstruction of firing temperatures was suggested by Goulpeau [ 28 ], who used it to distinguish between magnetic signals recorded when building materials were pre-fired and signals recorded when they were reheated to lower temperatures during the use of a Roman hypocaust.…”

“…Another method which has been applied for the estimation of heating temperature is thermoluminescence [13][14][15][16]. Rock magnetism can also be applied for estimating firing temperature by measuring susceptibility, hysteresis parameters or isothermal and anhysteretic remanences [1,5,15,[17][18][19][20][21][22]. Such magnetic methods are limited in identifying materials heated to 300-400C or lower and in accurately estimating these low heating temperatures [23].…”