The spark shower that is commonly observed when ferrous metals and other alloys are abraded is caused by the exothermic reaction of atmospheric oxygen with the freshly formed surfaces of the metal chips. This reaction greatly facilitates grinding as evidenced by a large increase in grinding forces when oxygen is removed from the tool-metal interface. Examination of grinding swarf combined with calculations of the kinetics of the oxidation reaction indicate that oxidation leads to increased plasticity of the metal during chip formation.Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference held in Atlantic City, New Jersey, October 8–10, 1968.