Hello Kubur,
My opinion is that this is task for the experienced restorer/conservator who has been working in some (army) museum for a longer time. already. It would be a pity to learn on some nice, old and valuable piece. If you donīt succeed, than you might have one piece as an "exclamation mark" (how not to do it next time) in your collection. I think it is worth to establish good relationship with such an expert and instead of buying another piece to invest in his work on your current piece. But, based on my own experience, I would only believe proofed expert (i. e working for the good museum longer time /two-three in the town/)).
In the case of a heavily corodated item, the silver and gold decoration, probably, is "undermined" with corrosion. If you do not stabilise this corrosion, the silver or gold coud fall off either immediately (when you clean it chemically without conversation/protecting/deactivating of undermined areas), or it could fall off after a years (if you just clean it mechanically, which may not touch you, but your successors).
Nevertheless I also tried to clean such items myself. I degreased the coftgari inscriptions with aceton or alcohol and covered it with a transparent lacquer, then (the lacqure should be removable with solvents). Than I tried to remove the rust mechanically with a special steel brushes used by goldsmith, around the inscriptions. If this did not help I used Chelaton III (trade mark used in the Czech Rep.) to remove the rust chemically - this is the most dangerous phase and I did it only when the inscriotion was covered by lacquer (which, probably, and I do not know if it was good or bad, soaked to the microscopic capilaries around and below . The result was acceptable (for me). But, still, I have doubts - I think that the corrosion below had also had to be pasivated chemically (e.g. by tanin), which I did I think only once. This definitely is not any "manual" or recommendation, jus a description how I did it. But, IMHO, you will never reach such result as a skilled museum worker, who has been restoring both for the deposit and the exhibitions. So it also depends how valuable is the piece, how you evaluate it.
Best,
Martin
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