The coloration of smalt produced at Ust-Ruditsa glass factory from 1753 to 1768

The color of glasses from Russian Ust-Ruditsa factory (1753 – 1768) containing copper depends on the amount of lead, ratio Cu2+/Cu+ and on the quantity of colorant added due to the shift of fundamental absorption edge and formation of nanoheterogeneous structure confirmed by RMBS-spectroscopy and TEM. [Display omitted] •Preparation of glasses having same composition of Ust-Ruditsa glass factory.•Analysis of the structure of glasses by TEM and RMBS spectroscopy.•Different coloration of glasses depending on the Cu and Pb concentrations.•Influence of copper on the potential of oxidation of the melt. The Ust-Ruditsa glass factory, founded in 1753 by the Russian scientist Mikhail Lomonosov has produced a variety of smalt glasses for mosaics and bijouterie. Lomonosov, which was the glass-technologist of the factory, by using a limited number of glass colorants elaborated the glass receipts with the aim to obtain colored glasses. At that site several hundred colored glasses were prepared, investigated and employed. We report and discuss here the use of copper as colorant in the preparation of glasses having the same composition of selected Ust-Ruditsa glasses. A series of K2O-PbO-SiO2 glasses (KPS) doped with copper 9.5K2O·xPbO·(90-x)SiO2·0.5CuO (x = 10.1, 19.0, 27.0, 38.0, 47.3, 52.1, 56.8, 61.4 % in mass) has been prepared by melt-quenching technique. The Brillouin and Rayleigh scattering was measured with a 532 nm laser by using the calculated glasses refraction indexes. We found that the color changes due to the bathochromic shift of charge transfer band with increasing lead concentration. The copper center coordination environment is always a distorted octahedron. Upon reduction of copper by carbon the melt glass changes to an opaque orange smalt coloration due to the presence of Cu2O dendrimers. The calculation of Landau-Placzek ratio shows a non-monotonic change with increasing lead concentration. The nano-heterogeneous structure of glasses, characterized by an elevated Landau-Placzek ratio, is confirmed by TEM.