The effects of nepheline syenite on the colorant behavior of porcelain stoneware tiles were assessed with special reference to the body composition. Potassium feldspar was replaced by nepheline syenite in a typical porcelain stoneware body by up to 15.6 wt.%. Technological parameters such as shrinkage, water absorption and porosity were measured. Phase composition and microstructural characteristics were determined to understand the role of nepheline syenite in the whiteness of a ceramic body. The results show that nepheline syenite had a significant effect on the sintering rate and influences remarkably the sintering behavior, increasing the shrinkage and decreasing total porosity. On the other hand there is a decrease in the amounts of mullite and quartz with addition of nepheline syenite. The bodies richer in nepheline syenite show larger amounts of albite and glassy phase. These bodies also present a higher whiteness with the same sintering conditions. The colorant characteristics appear to be directly related to the free albite crystals content. In conclusion nepheline syenite can be used in small amounts, 5 wt.%, to obtain an effective color development.

Keywords: Porcelain stoneware body, Nepheline syenite, Whiteness, Crystalline and glassy phase.