Non‐destructive Raman study of the glazing technique in lustre potteries and faience (9–14th centuries): silver ions, nanoclusters, microstructure and processing

Abstract

The oldest known nanotechnology dates back to the fabrication of the first lustre potteries. A lustre is a thin film formed just below the surface of medieval Islamic glazed potteries which contains silver and/or copper in the metallic and ionic form. Raman studies of the lustre films of different ceramics excavated from Fustât (near Cairo, Egypt, 11-12th century) or from the Silk Road (Termez, 13-14th centuries) showed that they associate many layers of different compositions (with or without cassiterite). Energy-dispersive spectroscopic analysis shows that all studied glazes are Ca-(and K)-rich, nearly free of Al silicates, with some addition of lead. Comparison is made with a copy of three-colour Tang ceramics made in Bassorah or Baghdad, in the 9th century, which is among the first known 'faiences', i.e. ceramics enamelled with an Sn-containing glaze. Surprisingly, Sn is not present in the form of a cassiterite (SnO 2 ) precipitate but as a Ca,K-rich salt. Composition analysis and Raman spectra show that all glazes have been processed with similar technology. The distribution of elemental Ag and Cu is very heterogeneous in the lustre decor. The main Raman signature (50-100 cm −1 peaks) of the lustre film is assigned to Ag + ions. The additional low-wavenumber features could be due to the Ag 0 [or (Ag n / m+ ] nanocluster modes. It is clear that the lustre colour arises from the combination of iridescence (diffraction) and absorption/diffusion. Raman criteria are proposed for a sample classification as a function of processing (cassiterite content, processing temperature). The glazing technique is discussed on the basis of experimental evidence and ancient potters' reports. Exothermic burning of acetate residus is proposed as the key step for the preparation of polychrome lustre.

Raman analysis of ancient pigments on a tile from the Citadel of Algiers

“…Fig. 8(a) shows a representative Raman spectrum collected from the white pigment that has been identified as cassiterite (SnO 2 ) [35] and Fig. 8(b) is that of the reference SnO 2 (Merck).…”

“…Raman measurements in this study prove conclusively that SnO 2 was deliberately used as the dominant component of the white glaze, in admixture with ␣-quartz. The glaze on this tile is similar to "faiences", ceramic where Sn-containing glazes are used [35]. It is also known that Fig.…”

Micro‐Raman and portable Raman spectroscopic investigation of blue pigments in selected Delft plates (17–20th Century)

“…Photographs were captured using an Olympus digital camera (Camedia C-7070) mounted on top of the microscope with an Olympus photographic eyepiece. Raman spectra were also recorded using the normal point-andshoot attachment, as well as the Nuscope attachment with XYZ www.interscience.wiley.com/journal/jrs [15] on the glaze surface and cassiterite, SnO 2 at 635 cm −1 [28,29] on the white slip. Raman spectra were obtained with 514.5 nm excitation, 3 cm −1 resolution (top).…”

“…Fifty micrometres into the glaze, the following components could be identified: alpha-quartz (460 cm −1 ), [26] feldspar [27] or cobalt blue (512 cm −1 ), [18,19] cassiterite (634 cm −1 ). [28,29] The silicate glaze is identified by broad bands around 500, 800 and 1000 cm −1 . This figure is available in colour online at www.interscience.wiley.com/journal/jrs.…”

Nanoparticles in Ancient Materials: The Metallic Lustre Decorations of Medieval Ceramics

“…Several descriptions of the glazing technique were proposed (Pérez-Arantegui, Molera et al 2001;Padeletti & Fermo 2003a;Colomban & Truong 2004;Pradell et al 2005;Roqué et al 2005;Pradell et al 2006;Roqué et al 2008;Colomban 2009) on the basis of experimental evidence and on information extracted from the transcription of ancient recipes (Abu al Qâsem 14 th century, Picolpasso 16 th century, Deck and Bertan 19 th century and Artigas 20 th century). Lustre decorations were obtained by applying a mixture of a paint, which contained copper and silver salts, water and more or less vinegar and lye, onto a glazed ceramic, which was subsequently annealed in a reducing atmosphere.…”