<b>Key Points</b>:</br> - Experiments on B2O3 evaporation from Ca- and Mg-bearing aluminoborosilicate melts were conducted at 1250 and 1350 °C for 60-1020 hours, under varying oxygen fugacities (FMQ-6 to FMQ+1.5) and in air.</br> - Results indicate that B evaporation increases by an order of magnitude under higher oxygen fugacities compared to reducing conditions, with two possible gas-phase speciation reactions for B2O3 suggested by Gibbs free energy minimization.</br> - B2O3 evaporation rate constants were calculated from the final glass compositions, showing slower evaporation rates than diffusion rates, indicating that evaporation is the rate-limiting process.