SOLUTIONS TO THE PROBLEM OF GLAZE ACCUMULATION AT TILE EDGES AND ASSOCIATED FAULTS.

P. Corma y L. Martínez (QPT), J. Martínez (Alquimia Técnica), Mª Dolores Llanes y V. Moreno (Rocersa), J. Vte. Carceller (Colorobbia), M. Gómez (Gres de Valls).

INTRODUCTION.

During ceramic tile manufacturing, glaze tends to accumulate at the tile sides. This accumulation can already be observed during glazing, but it becomes more obvious in the fired tile and may even reach aesthetically unacceptable limits.

These accumulations at the tile edges give rise to a series of problems:

- In the newly glazed tile:

• Difficulties in decorating and the appearance of faulty edges.

• Rise in the thickness ratio (glaze layer thickness/body thickness) in this area with regard to the rest of the tile and increased tendency to curl compared to other areas (presence of deformations).

- In the fired tile:

• Lack of surface flatness in the finished tile.

• Difficulties in surface grinding owing to different thicknesses.

• Difficulties in grinding and bevelling owing to differences in thickness and side deformation.

• Visual appearance of "topping" on the sides of the polished tile, joint area between the tiles.

• Tile side curling owing to the differential increase of the glaze layer in this area.

This defect is more apparent when considerable layers of glaze are applied, as is the case in bell glazing, typically used in single-fire wall tile production.

This effect is more clearly visible when transparent glazes are used as a result of the visual effect of the glossy surface.