COLOR IN CERAMIC GLAZES: efficiency of the Kubelka-Munk Model in glazes with a black pigment and opacifier

In this study the efficiency of the Kubelka-Munk model (already known and consolidated in other industrial sectors) was evaluated in the prediction of the colour of an opaque ceramic glaze obtained by a mixture of black pigment (spinel Ni-Fe-Cr) and zircon opacifier (ZrSiO4). Glazes with different percentages of black pigment and opacifier were prepared to determine the absorption and scattering optical constants from the reflectance curves measured with a spectrophotometer. After the physical and chemical characterization of the glazes components (frit, pigment and opacifier) suggestions for the adaptation of the Kubelka-Munk model were made to facilitate the experimental procedure of analysis. The result obtained with the adapted Kubelka-Munk model were in good agreement with the experimental reflectance curves. The reproduction of the desired colour was possible with a reduced number of experiments and the model made it possible to correlate the colour with the added pigments concentration facilitating the formulation step.