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Oxide system PbO-ZnO-B 2 O 3 -SiO 2 with the content of lead oxide of more than 45 mol.% is the basis of non-crystallizable low-melting glasses with softening temperature of lower than 450 0 Ñ. Lead-containing glasses are very aggressive, therefore they are melted in the platinum crucibles or ceramic crucibles which are resistant to the aggressive action of the lead glass melt. During the process of the melting of lead glasses in ceramic crucibles, the additives (Al 2 O 3 and SiO 2 ) are transferred from the crucible to the glass melt. An uncontrolled amount of these additives affects the properties of the glasses. The objective of this work was to establish the effect of the temperature-time conditions of melting on the physical and chemical properties of high-lead glasses prepared in both platinum crucibles and ceramic ones. The results of the study showed significant difference in properties of glasses synthesized in crucibles fabricated from different materials. Glass synthesized in the platinum crucible under various temperature-time conditions was characterized by stable physical and chemical characteristics and low softening temperature (~380 0°Ñ ) without any traces of crystallization under repeated heat treatment. The melting in the alumina crucible and quartz crucible under the same temperature-time conditions resulted in both a decrease in physical and chemical characteristics of low-melting glass and an increase in the glass softening temperature to 450-470 0 Ñ due to crystallization of glass during a heat treatment.

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New high-lead glasses with two different compositions are subjected to comprehensive material characterization. In particular, their refractive indices, optical transmission spectra, photo-elastic, piezo-optic and strain-optic constants, ultrasound velocities and elastic constants are measured. We find the shortwavelength absorption edges as λ edge = 383 and 475 nm for these compounds. The acousto-optic figures of merit are calculated for the glasses under study. Their maximal acousto-optic figures of merit turn out to be higher than the corresponding values for fused silica and dense flint glasses, which are known as vitreous materials widely used in serial acousto-optic modulators.