DOI: 10.1007/s00339-004-2508-2 Appl. Phys. A 79, 235–239 (2004) Materials Science & Processing Applied Physics A j. p ´ erez-arantegui 1, ✉ a. larrea 2 j. molera 3 t. pradell 4 m. vendrell-saz 3 Some aspects of the characterization of decorations on ceramic glazes 1 Departamento de Qu´ ımica Anal´ ıtica, Universidad de Zaragoza, 50009 Zaragoza, Spain 2 Instituto de Ciencia de Materiales de Arag´ on, Universidad de Zaragoza-CSIC, 50018 Zaragoza, Spain 3 Departament de Cristallografia i Mineralogia, Universitat de Barcelona, 08028 Barcelona, Spain 4 Department FEN, ESAB-CEIB, Universitat Politècnica de Catalunya, 08036 Barcelona, Spain Received: 11 June 2003 /Accepted: 15 December 2003 Published online: 19 May 2004 • © Springer-Verlag 2004 ABSTRACT From antiquity, glazes have been one of the tech- niques used for decorating ceramics. Potters took advantage of the optical properties of these glazes to improve the quality of the object, especially to obtain an appearance or some charac- teristics that had commercial success. This is why it is important to know the reasons of the visual appearance of glazes. In this paper we present some aspects of the characterization of lustre, one of the on-glaze decorations that results in a more spectacular visual effect, as a microstructure, its composition, its raw mate- rials and some technological aspects of its production. Lustre is a three-dimensional heterogeneous structure, where copper and silver nanoparticles play the most important role, but also al- kali elements in the glaze and other components of raw lustre pigments. Lustre properties are determined by copper and silver composition and by distribution and dimension of these metallic nanocrystals in the decoration layer. PACS 61.46.+w; 68.37.Hk; 68.37.Lp; 81.05.-t; 79.60.-i; 81.07.-b; 78.67.Bf; 81.05.Kf; 81.05.Je 1 Introduction The possibility of coating ceramics with glazes to decorate objects has been used since antiquity. Alkali glazes on clay bodies have been used in the Near East and Egypt since c. 1500 BC. The other main type of glazes, lead glazes (45%– 60% PbO), have probably been used from the Roman era (1st century BC) in the West and at the same period, or per- haps a few centuries earlier, in China. Another related group of glazes are tin-opacified glazes. Although initially (8th c. AD) they were alkali glazes containing only 1%–2% PbO, the lead content was progressively increased until they were lead–alkali glazes, containing typically 20%–40% PbO and 5%–12% alkali, by the tenth/eleventh century AD. This glaze type was used almost exclusively for the production of tin- opacified glazes throughout Near East and Europe [1]. Potters took advantage of the physical properties of glazes, especially some optical properties, to obtain a particular ap- pearance and other characteristic effects that led to a commer- cial success. This is why it is important to know the reasons ✉ Fax: +34-976/761292, E-mail: jparante@unizar.es of the visual appearance of glazes in their characterization. The composition of glazes on pottery settles a great part of the properties of the object, for example, high-lead glazes with a high refractive index produces shiny transparent glazes. But also glaze-body interaction and body composition are import- ant, not only for a good adherence of the glaze but for the transparency and glaze colour. In the case of high-lead glazes, the possibility of a great reaction between the clay body and the glaze can lead to the formation of a thick layer of crys- tals that leads to the loss of transparency and prevents the body colour from being seen through the glaze [2]. In tin-opacified glazes, potters preferred to apply glaze on a biscuit-fired body that reduces the interaction between glaze and body and con- sequently the introduction of new colouring elements from the body into the composition of the glaze [1, 2]. In other cases, as some incised-decorated ceramics from the Middle-East, a white slip was applied between body and glaze to prevent the glaze colour from being modified by the body colour [3]. In addition to the possibility that body colour takes part in the final visual aspect of the glazed object, glaze colour is espe- cially induced by the addition of metal ions (Cu(II), Fe(III), Fe(II), Co(II), etc.) dissolved into the glaze or by the pres- ence of crystalline compounds (cassiterite, chromite, etc.). Some elements, such as iron, with several oxidation states can even be used to modify colours without modifying glaze composition [4]. But one of the on-glaze decorations that gives a more spec- tacular visual result to ceramic objects is lustre due to its metallic shine and coloured iridescence. The earliest lustre was multicoloured: olive-green, brown, orange and yellow, whereas for centuries later lustre was almost always used as a single colour on each object [5, 6]. Among the different ceramic techniques often called as ‘lustre’, the decorative tradition, which is the subject of this paper, could be described as ‘reduced-pigment lustre’, that in- cludes all Islamic, Hispano–Moresque and Italian lustre ware. This lustre is made by applying some pigments (usually sil- ver and copper compounds) mixed with clay and ochre to the surface of an already-fired tin-glaze; then the ceramic piece is re-fired at a low temperature in a more or less reducing at- mosphere. The temperature and reducing atmosphere must be enough to produce the lustre decoration but also has to be con- trolled in order that the clay and the ochre do not adhere to the