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.

Five different mixed Al-hematites with an aluminium molar content varying from 0 to 10% were investigated by micro-Raman spectroscopy to study the effect of Al-for-Fe substitution on the hematite lattice. A red shift of hematite vibrational wavenumbers and a line broadening were observed; also a shoulder located near 430 cm −1 and a broad band at 670 cm −1 developed. The variation of the spectral features is discussed in terms of a local disorder correlated to the insertion of Al 3+ ions into the Fe(O) 6 octahedra constituting hematite structure. A multivariate analysis was also carried out on the spectral data to distinguish between the doped samples analysed.

In this project, micro-Raman (µ-Raman) spectroscopy has been used as a means to investigate the pigments employed in decoration of Anasazi pottery. Analysis of Raman spectra revealed the presence of organic-(amorphous carbon), iron-and/or manganese-based pigments in line with the known pictorial materials used by Anasazi people. The results were also complemented by studies employing a scanning electron microscope equipped with a microanalysis energy dispersive X-ray detection (SEM/EDX) system, which proved helpful mainly while identifying the manganese-based minerals (i.e. pyrolusite). Knowledge of the pigments augments our understanding of the materials favored by the different production centers and of the artistic skills of ceramic producers.

Micro-Raman spectroscopy was applied to the study of some French sigillata wares dating back to the end of the 1st century AD and coming from two important Roman ceramic production centres at La Graufesenque (Aveyron) and Glanum in Saint Rémi de Provence. The differentiation between the mineralogical composition of the reddish bright slip and the porous ceramic body underneath was accomplished, confirming the previous hypothesis by the CNRS research group at Toulouse that a different and finer clay material was used for the coating. This was primarily suggested by the highly heterogeneous body matrix mineralogy due to the presence of a large variety of minerals such as haematite, quartz, rutile and feldspar species, while the slip coating was basically made of haematite alone. The phase analysis results also gave an indication of the firing for insight into the production technology: an oxidizing atmosphere and a firing range between 850 and 1000 • C could be suggested, in good accordance with the acknowledged Roman sigillata pottery production procedure.

SERDS (shift excitation difference spectroscopy) and SSRS (subtracted shifted Raman spectroscopy) methods were applied for fluorescence-background rejection in the Raman spectra of colored materials. These techniques are based on the assumption that the fluorescence contribution can be completely eliminated by subtracting two Raman spectra acquired at two shifted laser excitation frequencies. For the SERDS method a micro-Raman experimental apparatus coupled with a tunable diode laser (central emission at 684 nm) was set up. SSRS measurements were made on a commercial micro-Raman instrument; in this case the shifted spectrum was obtained by moving the spectrometer grating. Raman spectra were then reconstructed by applying the difference deconvolution method that automatically converts the difference signals in Raman peaks through a deconvolution operation. These techniques were tested on two reference colors (ultramarine and 6,6 -dibromoindigotine) and two colored samples of unknown composition (a Pompeian pink powder and a blue paint from a XVII century painting). Fluorescencebackground subtraction and the following operation of spectra reconstruction took place successfully with no errors in Raman peaks, width and wavenumber position. In addition, even weak spectral details were revealed favoring the comparison with reference data for a molecular identification.