Efecto del Tipo de Defloculante y del Óxido de Hierro sobre el Color y Absorción de Cerámicas Engobadas

In this study, the type of deflocculant and the proportion of iron oxide are modified to analyze the color using the CIELab model and the water absorption of the engobe-coated ceramics. The levels investigated for iron oxide were 2.5, 5, and 10%, and for the type of deflocculant: sodium silicate, sodium carbonate, and sodium hexametaphosphate. To establish the optimum percentage of the dispersion agent, deflocculation curves were created, with results of 0.44% for sodium silicate, 0.15% for sodium carbonate, and 0.22% for sodium hexametaphosphate. Engobes were made in an alumina ball mill with a mixing time of 15 minutes. The supports were dip-coated; each support received three layers of coating that were immersed for no more than three seconds. The dried engobed tesserae were fired at 950°C after one week of drying. Color was measured using ASTM D 2244, and the percentage of water absorption was determined using ASTM C 373. The results show that the saturation of the engobes increases with the percentage of iron oxide, but not with brightness, hue, or absorption, which decrease. In addition, sodium silicate shows the most promising results as a deflocculant because it disperses more fine particles on the surface, improving color parameters and decreasing water absorption.