...Since the surface film is thin and loosely bound, it is subject to any mechanical abrasion and/or acid attack. A top film is required to protect it - poly, wax, drying oil, etc. Anything that removes "rust" is very likely to attack CCH; either chemical or mechanical. The only advice I can give is to go slow and be careful. Keep experiments as small and inconspicious as possible.
Dr Gaddy published SEM photos of case coloring. As Don states, this is very thin, only a few atoms thick. That is why a protective coating is always applied.
Pete
