Isn't there some way to chemically 'passivate' the polished surface? Maybe a phosphoric acid pickle, or something?
I have 3 older British boxlocks with an 'in-the-white' finish, and there does not appear to be any coating such as lacquer or wax on them. I suspect that they were originally case colored, but I can find no trace of any color left. Interestingly, they do not seem to be any more succeptable to tarnish, discoloration or rust than my case colored guns.
I would be very interested to find out what is (or was) done to them, if someone knows what how these guns may have been processed.
