Stain resistance is one of the most important properties of porcelain stoneware. It is directly related to the porosity of the material. The design of experiments (DOE) approach can be used to optimise the production of porcelain stoneware. The effect of compaction pressure, temperature and time at the maximum temperature in the firing cycle was studied using two-level full-factorial experimental design. The parameters were fixed according to the industrial values used in producing porcelain stoneware tiles. Their influence on stain resistance was determined using spectrophotometry. A mathematical model was used and experimentally verified. The results are presented and discussed. Good agreement was obtained between calculated and experimental values, with a high coefficient of correlation.