A method of producing a reflector sheet, which method comprises treating an Al alloy sheet to increase the total reflectance of a surface of the sheet for use as a lighting reflector by bringing the sheet into contact with an acid or alkaline fluid that dissolves aluminium metal, said fluid having a viscosity of less than 0.01 Pas, under conditions to remove from 10 nm to 2000 nm of metal from the surface, and cutting or forming the treated Al alloy sheet into the shape of a reflector sheet.