Abstract: The invention concerns a sealing method for producing a film of oxide having good saline corrosion resistance properties on a metal substrate. Said method comprises steps consisting of: providing a buffered sealing solution comprising at least one simple cobalt II salt and at least one simple lithium III salt; and bringing said metal substrate having a previously oxidized surface into contact with said sealing solution for a period sufficient to form a mixed cobalt/lithium oxide film. More particularly, this method is applicable to a metal substrate produced from aluminum or from aluminum alloy anodized in a sulfuric medium.