A new nitriding method has been devised which requires only a simple vacuum furnace and enables direct nitridation of solid aluminium without any prior surface treatment. It can be used to produce thick aluminium nitride surface layers on aluminium, under nitrogen at atmospheric pressure. A critical element of the process is the use of a magnesium vapour source that reduces/disrupts the natural, protective oxide film on the aluminium surface and facilitates nitriding. The nitride surface layers form through two distinct modes, one growing outward from the aluminium plate surface and the other growing into the aluminium. Studies of the nitride layers utilizing optical microscopy, TEM, SEM, XRD and XPS have been conducted. Details of the composition, structure and growth as well as possible mechanisms for the nitride formation are presented. Understanding of the reaction may have important implications for the production of wear resistant coatings on bulk Al as well as for the production of Al/AlN composites.