Issue No. 2

Abstract

At present new aesthetic effects are being sought by polishing the glaze surface. The tiles that are polished can have very thick glaze layers (of the order of 1 mm thickness) produced by dry application of granulars, or finer layers (of the order of 300 μm) applied by the wet method. In the first case, surfaces with specular gloss are achieved, on removing half the original thickness. In the second case, polishing removes between 30 and 50 μm of the glaze layer, providing it with a satin finish. Polishing opens some of the pores occluded in the glaze, converting part of the initially closed porosity into apparent porosity, capable of retaining dirt. Polished surface porosity is determined, amongst other factors, by glaze inner porosity.

Abstract

This work describes the crystal chemistry of synthetic mullite doped with Fe, Mn, Cr, Co, V, Pr, Cd, Ni, Cu, Zn and Zr. The synthesis was achieved at 1500 °C for 4 h starting from caolinite and aluminum hydroxide. The solubility of the doping element in mullite was investigated. Synthetic mullites can be classified with respect to their degree of crystallization: (1) good crystallization (Fe-, Mn-, V-mullite); (2) rather good crystallization (undoped-, Cr-, Co-, Ni-, Pr-, Zn-, Zrmullite); (3) poor crystallization (Cd-, Cu-mullite). The application of mullite as a bulk pigment in stoneware products and as a component for “matt” glazes was promising only for the latter application.

Abstract

The technological aspects in the application of MaxxMillÒ (as a refining mill) in the final grinding of porcelain stoneware tile slips produced with both continuous and discontinuous ball mills were investigated. The experiments, carried out in an Italian ceramic floor and wall tile company, were focused on the cost effectiveness of the improvements in fineness of grinding and grinding efficiency that can be achieved using MaxxMillÒ. The energy savings obtained were quantified and other benefits are discussed.

Abstract

The latest phase of the restoration interventions on the mosaics of the basilica of San Vitale in Ravenna, which were carried out in the period 1988-1999, concerned the wall mosaics of the Justinian and Theodora’s panels. Samples of glass tesserae from these panels have been chemically analysed by spectroscopic methods. The knowledge of the chemical composition of these glasses has allowed to enrich the already considerable extent of the database relative to the mosaic glasses of the decoration of the basilica. On the other hand, it was possible to recognize and distinguish glasses produced with different technologies and raw materials, thus dated to different periods. A particular attention has been paid to the identification of the typologies belonging to the original production and, considering only these glasses, a study has been carried out on the origin of the colouring.