An aluminium-wettable protective coating on a substrate, for use at elevated temperature in an oxidising and/or corrosive gaseous and/or molten environment is disclosed. The coating (20A, 20B, 20C, 20D) is applied to protect the substrate (5, 15, 16) from liquid and/or gaseous attack. The coating comprises particles of at least one metal oxide and/or at least one partly oxidised metal in a dried and/or cured colloidal carrier and/or organic binder. The metal oxide and/or partly oxidised metal is reactable with molten aluminium when exposed thereto to form an alumina matrix containing metal of said particles and aluminium. The coated substrate (5, 15, 16) may be used in an aluminium electrowinning cell, an arc furnace for the recycling of steel or an apparatus for the purification of a molten metal such as aluminium, magnesium, iron or steel.