<p>The present study focused on phase equilibria in the PbO–AlO_1.5 and PbO–AlO_1.5–SiO₂ systems. The equilibration and quenching technique followed by the electron probe X-ray microanalysis (EPMA) was used in the present study. The liquidus of the PbO–AlO_1.5–SiO₂ system in air, including corundum (Al₂O₃), cristobalite/tridymite/quartz (SiO₂), feldspar (PbAl₂Si_2+<i>x</i>O_8+2<i>x</i>), massicot (PbO), mullite (Al_6+2<i>x</i>Si_{2−2<i>x</i>}O_{13−<i>x</i>}), PbAl₁₂O₁₉, PbAl₂O₄, Pb₉Al₈O₂₁, Pb₆Al₂Si₆O₂₁, Pb₄Al₂Si₂O₁₁, Pb₄Al₄Si₃O₁₆, Pb₃Al₁₀SiO₂₀ and Pb₁₂Al₂Si₂₀O₅₅ primary phase fields, has been characterised. New lead aluminosilicate compounds, Pb₁₃Al₄Si₆O₃₁, Pb₁₂Al₆Si₁₀O₃₁, Pb₉Al₄Si₈O₃₁, Pb₇Al₂Si₈O₂₆ and Pb₇Al₂Si₁₀O₃₀ were found to coexist with oxide liquid. The PbO–AlO_1.5 binary and PbO–AlO_1.5–SiO₂ ternary systems in air were reoptimized based on the obtained experimental data. New experimental results together with phase equilibria and thermodynamic literature data were used to obtain a self-consistent set of parameters of the thermodynamic model for all phases of the PbO–AlO_1.5–SiO₂ system in air. The predicted liquidus projection of the PbO–AlO_1.5–SiO₂ system was presented for the first time in the full range of temperatures and compositions.</p> Graphical Abstract <p></p>