Structural characterization of the glassy phase in majolica glazes by Raman spectroscopy: A comparison between Renaissance samples and replica processed at different temperatures Camilla Ricci a , Costanza Miliani b, * , Francesca Rosi a , Brunetto G. Brunetti a , Antonio Sgamellotti a,b a SMAArt, Dipartimento di Chimica, via Elce di sotto 8, 06123 Perugia, Italy b CNR-ISTM, Dipartimento di Chimica, via Elce di sotto 8, 06123 Perugia, Italy Received 8 November 2005; received in revised form 11 December 2006 Available online 7 March 2007 Abstract Tin-opacified lead glaze, prepared according to Renaissance recipes, has been fired at different temperature from 300 °C to 990 °C, and investigated by Raman scattering. A chemometric treatment and a systematic curve-fitting procedure have been applied in the range of 700–1250 cm 1 in order to monitor quantitatively the structural changes of the silicate network that occurred with firing. The results obtained on model glazes are compared with Raman spectra collected on various Renaissance potteries. This method is suggested for non-invasive surface analysis of ancient glazes aimed at the characterization of processing techniques. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Glass ceramics; Raman scattering; Archaeology; Raman spectroscopy; Aluminosilicates 1. Introduction Glaze is essentially a vitreous covering enveloping and decorating the surface of a ceramic body. It is made up of siliceous sands and borax; potash, soda and lead oxides are added to decrease the melting point of the mixture in such a way as not to modify the ceramic body [1] during the double fired techniques. Historically, during middle Ages, in the Mediterranean basin silica-based glazes were applied on pottery both to make watertight containers and to decorate the artefact. Several glazed forms colored with a range of pigments, both crystalline and amorphous, were produced and obtained in different ways. The interest in micro-Raman spectroscopy as a tech- nique for the characterization of historical glazes has been recently demonstrated by Colomban and co-workers [2– 5]. It appears to be unique for detecting structural phases because of its capabilities: microanalysis for both crystalline pigments and glassy phases is permitted, the measurements are non-destructive, the optically confocal system of a Raman micro-spectrometer enables one to search structural phases along the sample thickness. For glassy phases, a dif- ferentiation between the various aluminosilicate networks of glazes on the basis of Raman spectra is possible because the connectivity of the SiO 4 polymeric units can be investi- gated through the Si–O stretching and bending modes, around 1000 and 500 cm 1 , respectively. Using a curve fit procedure, Raman spectra of the glassy phases are usually deconvoluted into the Q n components which are statistically characteristic for certain glazes and their related technol- ogy. The structure of glasses is a function of two factors: bulk composition and temperature of melt equilibration. On the basis of previous papers of Colomban that focused the attention on bulk composition factor ranging from alka- line Islamic enamels to modern porcelain glazes [6], we have taken into consideration the temperature factor on a typical composition of Renaissance majolica lead glaze. 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.12.099 * Corresponding author. Tel.: +39 0755855639; fax: +39 0755855606. E-mail address: miliani@thch.unipg.it (C. Miliani). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 1054–1059