An apparatus for coating a substrate with an alumina hydrate film includes a coating vessel having at least one support therein; the substrate to be coated is mounted on the support; and at least one porous or perforated container for holding aluminum metal to react with a caustic solution to form an aluminate coating solution is also mounted on the support. The apparatus can also contain means for mechanical agitation, such as a rotational stirring device. In the coating of the substrate a caustic solution is contacted with a substrate and with at least one porous container having aluminum metal therein. The aluminum metal reacts with the caustic solution to form an aluminate coating solution and then an alumina hydrate film is deposited on the substrate. The caustic solution is preferably subjected to mechanical agitation during the coating process.