Phase equilibria of the “Cu2O”–Al2O3–SiO2 system have been experimentally investigated at metallic copper saturation. High-temperature equilibration, rapid quenching, and electron probe X-ray microanalysis (EPMA) techniques have been used. Containerless equilibration technique has been developed to enable the phase equilibrium of this chemically reactive system to be investigated. The microstructures and compositions of all phases present in the quenched sample were measured accurately using EPMA. The isothermals between 1150°C and 1300°C have been determined in the “Cu2O”–Al2O3–SiO2 system at metallic copper saturation. The following primary phase fields were identified in the system: SiO2 (tridymite), Cu2O (cuprite), Cu2O.Al2O3 (delafossite), Al2O3 (corundum), and 3Al2O3·2SiO2 (mullite). The implications of the phase diagram on making of the copper aluminosilicate glass have been demonstrated.