The use of chromic acid, instead of the normally used sulfuric acid, leads to a slight difference of these oxide layers.
From the en.wikipedia.org
The chromic acid coats the aluminum with a thin layer of chromate material, making it resistant to corrosion.
From the sciencedaily.com
Exceeding these concentrations results in deposits of chromic acid in the dried film which ruins any attempts at printing.
From the en.wikipedia.org
Chromic acid is a powerful oxidizing agent and is a useful compound for cleaning laboratory glassware of any trace of organic compounds.
From the en.wikipedia.org
Roy Beck, Charles Peter and Edward Owens studied and experimented with chromic acid salt sensitized emulsions for photo-reactive stencils.
From the en.wikipedia.org
Anodizing of aluminium is another electrochemical process, which does not lead to the deposition of chromium, but uses chromic acid as electrolyte in the solution.
From the en.wikipedia.org
Expanded graphite is made by immersing natural flake graphite in a bath of chromic acid, then concentrated sulfuric acid, which forces the crystal lattice planes apart, thus expanding the graphite.