Evaporation processes and thermodynamic properties were for the first time investigated using the Knudsen effusion mass spectrometric method for ceramics based on the Cs2O—Al2O3—SiO2 system within the temperature range of 1000–1200 K. The found values of partial pressures of vapor species, activities of components, and Gibbs energy indicated negative deviations of the thermodynamic properties from the model of ideal solution. The obtained experimental values of thermodynamic properties were optimized using the generalized lattice theory of the associated solutions. © 2025 Elsevier B.V., All rights reserved.