Transparent high lead and tin-opacijied lead-alkali glazes have been extensively used throughout Europe and the Near East from theirjrst appearance in the Roman era and the tenth-to eleventh-century Islamic world, respectively, up until the present day. Using, to a large extent, information which is widely scattered through a diverse range of literature, the methods employed in the production of these two glaze types arejrst outlined and their merits are then compared with those of alkali glazes in terms of ease of preparation of the glaze mixture, ease of application of the glaze, ease ofjring, cost of production, glaze-body j t and visual appearance. The principal advantages of transparent high lead glazes as compared to alkali glazes are shown to be ease ofpreparation and application of the glaze suspension, low susceptibility to glaze 'crazing' and 'crawling' and high optical brilliance. Factors that influence the choice of tin-opacijied lead-alkali glazes include ease of production of tin oxide by melting tin and lead metals together; a reduced risk of reduction of lead oxide to lead metal and consequent blackening of the glaze; and, again, low susceptibility to 'crazing' and 'crawling'. Limits of current knowledge regarding these two glaze types and requirements for future research are outlined.

A set of laboratory experiments has been developed to determine the nature and importance of the interaction between clay bodies and lead glazes during firing following different thermal paths (firing time and temperature, cooling rates) and using different glaze compositions and different bodies (illitic, kaolinitic, and calcareous clays). It is shown that the interaction consists of a digestion/diffusion process. This process involves (i) decomposition of the phases forming the clay body (digestion), (ii) chemical diffusion of elements between clay body and glaze, and (iii) formation of a layer (interface between clay and glaze) of small K-Pb feldspar crystallites.

Luster is a decorative metallic film that was applied on the surface of medieval glazed pottery. It can be obtained via the low-temperature (ϳ650°C), controlled reduction of copper and silver compounds. In this paper, we show that luster is a thin layered film (200 -500 nm thick) that contains metallic spherical nanocrystals dispersed in a silicon-rich matrix and has a metal-free outermost glassy layer that is 10 -20 nm thick. Silver nanocrystals seem to be separated from those of copper, forming aggregates 5-100 m in diameter. This composite structure exhibits optical properties that are dependent on both the particle size and the matrix. Luster is indeed the first reproducible nanostructured thin metallic film that was made by humans.

Analysis of medieval luster ceramics seems to indicate that the formation of luster layers could involve an ion exchange between some alkali ions of the glaze (Na+ and K+), and copper and silver cations of the luster raw paint during firing. However, because of the weathering shown by the medieval luster decorations analyzed, conclusive proof is difficult to obtain. A realistic reproduction of the luster decorations has been fabricated in order to follow the process of formation of the luster layer. This has been studied by optical microscopy, transmission electron microscopy, electron probe microanalysis, extended X‐ray absorption fine structure, X‐ray absorption near‐edge structure, and the results give direct evidence that ion exchange and diffusion are the physical–chemical mechanisms responsible for the introduction of copper and silver into the glaze.