This study describes the role of nickel oxide (NiO) in peraluminous glass. Peraluminous glass is defined by an excess of aluminium ions (Al3+) compared to modifier elements such as Na+, Li+ or Ca2+ ions. The study investigates the effect NiO incorporation on peraluminous glass homogeneity and process ability. Quenched NiO-containing glass showed an incorporation limit greater than 12 wt% NiO (13.8 mol%), while slowly cooled glass showed a limit of 5 wt% NiO (5.8 mol%). Nickel oxide is also found to have a fludifying effect on peraluminous glasses. When the nickel oxide content is above its incorporation limit, the resulting crystals were found to have a significant effect on glass rheological properties. Finally, hypotheses are proposed as to the structural role of Ni in peraluminous glass based on the experimental results obtained. •The effect of NiO incorporation on peraluminous glass homogeneity and process ability is investigated•Quenched glass showed an incorporation limit greater than 12 wt% NiO (13.8 mol%)•Slowly cooled glass showed an incorporation limit of 5 wt% NiO (5.8 mol%)•NiO is found to have a fludifying effect•Ni-containing crystals were found to have a significant effect on the glass rheological properties•Hypotheses on the structural role of Ni in peraluminous glass are proposed