Assessment of a testing protocol for glazes characterization in view of their use on ceramic tiles

Italian ceramic tiles are worldwide recognized as top level products for theirtechnological characteristics as well as for their decoration that involve the use ofhigh-quality glazes. For market purpose, ceramic tiles need to be tested according to standardizedtesting methods as prescribed by ISO 13006 and EN 14411.These two standardsfi x the requirements and the corresponding test methods at the international andEuropean level, respectively, and some of these tests are mainly addressed tocharacterize ceramic tile surfaces (e.g. surface abrasion test, scratch resistancetest, etc.). However, for glaze development, other analytical tests, such as opticaland scanning electron microscopy, microhardness and XRD analyses, may be moreeffi cient to establish if glaze properties allow to reach the desired performances inthe fi nal product. The aim of this work is to set up a testing protocol for glazecharacterization which takes into account the needs of ceramic tile sector(standards requirements) as well as the fundamental parameters that shall beknown to improve glaze characteristics (e.g. hardness, wear, etc.). Thus, theresearch carried out was based on the comparison of the results obtained withanalytical tests on fi ve different commercial glazes with the ones found on ceramictiles decorated with the same glazes by applying some standardized test methodsrequired by the market. The commercial glazes have been applied on porcelain stoneware ceramic body byairless technique in the amount of 440 g/m2 with a density of 1450 g/L. Glazedspecimens were fi red at 1205°C for 50 min using a fast-fi ring cycle. Analysesconducted on the sample surfaces highlight a relationship between hardness andgloss. It was observed that specimens with high hardness exhibited a low glosslevel appearing matte, whereas specimens with lower hardness showed a highgloss level, resulting translucent. Microstructural investigation revealed a veryheterogeneous microstructure for the hardest sample, consisting of crystallinephases (clusters of barium- and calcium-based crystals)dispersed in theamorphous matrix, while the softest one was mostly amorphous. Technological properties like abrasion, impact and wear resistance weredetermined according to test methods described in ISO EN 10545 standards. Boththe impact and the abrasion test were not anyway able to discriminate between theinvestigated glazes, whereas interesting results were obtained by using a novelmulti-attribute method which is currently under development as standard. Parameters derived from the implemented characterization protocol would be usedin future research in order to design and produced glaze with enhanced andoptimized mechanical and tribological properties.