Despite recent advances, glass still breaks. This remains a major limitation for cover glasses used, for instance, in smartphone screens. Here, the authors explore the possibility of benefiting from nanoscale phase separation to significantly increase the fracture toughness of glass, while retaining its transparency. Based on peridynamic simulations, they investigate the nature of the toughening mechanisms at play and find that nanoscale phase separation can yield up to a 90% increase in fracture energy. This establishes phase separation as a promising route to develop novel tough, yet transparent glasses