A method of forming a coating on a metal article, wherein the coating is for protecting the underlying metal article against materials that are corrosive to the metal, the method comprising the steps of: a) anodizing the surface of the metal article by applying a voltage to the metal article, wherein the voltage parameters used for anodisation are selected to homogenise the surface layer, to produce a subcoating on the substrate, by performing the anodizing step in two stages; a first anodizing stage where an electric potential is applied to the substrate for homogenization of the surface layer and a second anodizing stage where an electric potential is then applied to the substrate to form a protective sublayer, wherein the electric potential during the first anodizing stage is varied according to a first voltage profile which includes an increasing potential between 0 and 2 Volts, wherein the potential during the second anodizing stage is varied according to a second voltage profile which includes an increasing potential between 0 and 20 Volts, wherein the pores are irregular tortuous branched cracks that reach through to the underlying metal article, b) depositing by atomic layer deposition on the anodized subcoating to add a top-layer of a second material which is not corroded by materials that would corrode the underlying metal article, such that the entire surface is covered by the second material including the walls down to the bottom of the irregular branched pores even when they are long and narrow and have a complicated 3D geometry but without closing or corking the pore's openings to protect from dissolving the underlying anodised layer by preventing materials that would otherwise corrode the underlying metal article from reaching the underlying metal article. a) anodizing the surface of the metal article by applying a voltage to the metal article, wherein the voltage parameters used for anodisation are selected to homogenise the surface layer, to produce a subcoating on the substrate, by performing the anodizing step in two stages; a first anodizing stage where an electric potential is applied to the substrate for homogenization of the surface layer and a second anodizing stage where an electric potential is then applied to the substrate to form a protective sublayer, wherein the electric potential during the first anodizing stage is varied according to a first voltage profile which includes an increasing potential between 0 and 2 Volts, wherein the potential during the second anodizing stage is varied according to a second voltage profile which includes an increasing potential between 0 and 20 Volts, wherein the pores are irregular tortuous branched cracks that reach through to the underlying metal article, b) depositing by atomic layer deposition on the anodized subcoating to add a top-layer of a second material which is not corroded by materials that would corrode the underlying metal article, such that the entire surface is covered by the second material including the walls down to the bottom of the irregular branched pores even when they are long and narrow and have a complicated 3D geometry but without closing or corking the pore's openings to protect from dissolving the underlying anodised layer by preventing materials that would otherwise corrode the underlying metal article from reaching the underlying metal article.