Micro‐Raman study of aluminium‐bearing hematite from the slip of Gaul sigillata wares

Abstract

Abstract The presence of sub‐microscopic Al‐Fe2O3 and Fe‐Al2O3 impure crystallites in the slip of sigillata wares from La Graufesenque (southern France) has recently been demonstrated by micro‐structural analyses, posing new questions about manufacturing processes and technological skills. To clarify the chemical composition and the spatial distribution of such phases within the slip, five representative sigillata wares were investigated by micro‐Raman spectroscopy. The recorded spectra show the typical hematite bands, though the Raman peaks are broadened and shifted, which agrees with a disordered phase. This is also reflected in a signal at 670 cm−1, while a shoulder close to 430 cm−1 is attributed to point defects, in agreement with the substitution of Fe atoms by Al atoms. A corundum spectrum was not detected indeed, probably hidden by the more intense hematite one. Spectral parameters were then estimated by a curve‐fitting analysis. Their comparison indicates a similarity among the investigated slips as well as uniformity within the slip layer. This suggests an awareness of the control of the production process among the local craftsmen. The spectral interpretation was assisted by reference spectra acquired on artificially doped hematite and corundum powder samples, which were used for probing the doping effect on the vibrational features of the pure crystallites. Copyright © 2006 John Wiley & Sons, Ltd.

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