18thC Ottoman Flintlock Holster pistol restoration project.

[Matchlock]

As to possible damage, we should differentiate varios forms of rust.

Removing aggressive red surface rust does, in my experience, not need chemicals but just oil. Oiling will passivate it.

Old, plain and black rust is stable in itself and does not need any treatment except oil.

I dare repeat my credo once more: chemicals will irreversibly ruin and spoil old surfaces. I would always prefer a heavily patinated, dark iron surface to any bright polish. Its impression is much closer to the original period surface, and you can always take something off but hardly add anything!

Don't forget that these items have come down to us unrotten since hundreds of years in untouched condition. We won't live to see them vanish under our hands even if we preserve their charming old surfaces.

Best,
Michael