To lighten the mood a bit, I'll tell you a story. In 1990, Dr. Sempé passed away, and his widow, fearing theft, hid his Andean archaeology collection, along with 70 tsuba and kozuka, behind a platform in their country house. Thirty-five years later, their daughter-in-law undertook renovations and rediscovered these completely forgotten collections. Naturally, all the tsuba and kozuka were corroded with numerous spots of red rust. Last Friday, I bought three of these tsuba at an auction. Here are photos of one of them before and after the cleaning I performed (washing with soapy water, scraping off the rust with bone, then lightly oiling).
No corrosive products were used, of course