Aluminium workpiece

This invention concerns aluminium workpieces, particularly aluminium sheet, mainly thin sheet used for containerstock or as foil. Containers are often subjected to abrasion during transportation prior to filling. An aluminum workpiece, e.g. sheet for containerstock, having an anodic oxide film whose thickness varies from location to location on the surface, whereby interference contrast effects are visible on the surface. Aluminum foil having on a surface thereof an unsealed anodic oxide film 5-1000 nm thick which provides a clean surface with fretting resistance. A method of anodizing thin aluminum foil is also described.