Could EDTA gel work maybe?
See: 
https://www.youtube.com/watch?v=WhzNttK_-ko
He says it works on a tulwar with koftgari:
https://www.youtube.com/post/UgkxPCh...NeHHJ0hiXzBMGr
	Quote:
	
	
		
			
				The EDTA gel seems to work on koftgari. Modified with sodium bicarbonate to slightly above neutral pH, did not affect the cross-hatching or iron oxides below the koftgari. 
 
The silver overlay remained grey after gel removal but rapidly brightened when wiped with oil. Two or three gentle passes of a paper towel, in circular motions, and the silver oxidation was removed.
			
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