Boron suboxide powder has been prepared by the reduction of metal oxides, usually ZnO, but also by MgO, SnO, Ga2O3 and CdO, with boron. Massive boron suboxide can be prepared by hot pressing; sintering occurs at 1600°C, i.e. 200°C lower than reactive hot pressing. In a study of the reaction of boron with boron anhydride B2O3, with graphical data processing, three characteristics stages are observed 1. (a) fusion of B2O3 at low temperature, 2. (b) reaction at about 1200 °C and 3. (c) densification of B12O2 at 1800 °C. The final product is always crystallized B12O2 containing an amorphous phase. It appears that this phase could be boron clusters bound with oxygen according to the variation in the O-B ratio observed without significant change in the rhombohedral cell dimensions.