Electroluminescence of aluminium during electropolishing in nitric acid

Electropolishing of aluminium in 10 mol dm-3 aqueous nitric acid shows the emission of electroluminescence. The very high anodic current densities involved during electropolishing preclude the presence of all but the thinnest of surface oxide films, and this raises the question of the origins of the luminescence. The electroluminescence during electropolishing is compared with that occurring during anodising in phosphoric acid.