Spectroscopic analysis of blue cobalt smalt pigment

The method for the determination of SiO2 in physical mixtures of CoO and SiO2 or blue cobalt smalt pigment (CoO·nSiO2) by FTIR spectroscopy is suggested. The infrared spectra of all samples were recorded using KBr pellets. It was demonstrated that the characteristic Si–O absorption band at 812 cm−1 could be successfully used as indicator in the evaluation of molar ratio of CoO and SiO2 in their mixture and pigment CoO·nSiO2. The integrated peak area linearly depends on the mole fraction of SiO2 in the physical mixture of CoO and SiO2 (in the range of 9.1–50%), and in the cobalt pigment smalt synthesized at 850–900 °C (in the range of 20–50%). Therefore, FTIR spectroscopic evaluation of CoO·nSiO2 samples provides a possibility to determine the chemical composition of historical cobalt smalt pigments. In addition, the suggested technique is simple, fast and sufficiently accurate.