Italian ceramic tiles are worldwide recognized as top level products for their technological characteristics as well as for their decoration that involve the use of high-quality glazes.
For market purpose, ceramic tiles need to be tested according to standardized testing methods as prescribed by ISO 13006 and EN 14411.These two standards fix the requirements and the corresponding test methods at the international and European level, respectively, and some of these tests are mainly addressed to characterize ceramic tile surfaces (e.g. surface abrasion test, scratch resistance test, etc.). However, for glaze development, other analytical tests, such as optical and scanning electron microscopy, microhardness and XRD analyses, may be more efficient to establish if glaze properties allow to reach the desired performances in the final product. The aim of this work is to set up a testing protocol for glaze characterization which takes into account the needs of ceramic tile sector (standards requirements) as well as the fundamental parameters that shall be known to improve glaze characteristics (e.g. hardness, wear, etc.). Thus, the research carried out was based on the comparison of the results obtained with analytical tests on five different commercial glazes with the ones found on ceramic tiles decorated with the same glazes by applying some standardized test methods required by the market.
The commercial glazes have been applied on porcelain stoneware ceramic body by airless technique in the amount of 440 g/m2 with a density of 1450 g/L. Glazed specimens were fired at 1205°C for 50 min using a fast-firing cycle. Analyses conducted on the sample surfaces highlight a relationship between hardness and gloss. It was observed that specimens with high hardness exhibited a low gloss level appearing matte, whereas specimens with lower hardness showed a high gloss level, resulting translucent. Microstructural investigation revealed a very heterogeneous microstructure for the hardest sample, consisting of crystalline phases (clusters of barium- and calcium-based crystals)dispersed in the amorphous matrix, while the softest one was mostly amorphous.
Technological properties like abrasion, impact and wear resistance were determined according to test methods described in ISO EN 10545 standards. Both the impact and the abrasion test were not anyway able to discriminate between the investigated glazes, whereas interesting results were obtained by using a novel multi-attribute method which is currently under development as standard.
Parameters derived from the implemented characterization protocol would be used in future research in order to design and produced glaze with enhanced and optimized mechanical and tribological properties.