I have several antiques that I have not touched other than cleaning the dirt off with soap and water, and I won't go beyond that. But I also obtained an H.Aston that was a rusty piece of junk, worth maybe $200. A few places told me to clean it up, which I did, and now it's probably worth $500 plus, depending on the market. It's not a rare or unusual piece to begin with. I also bought a 50-70 Trapdoor that needed cleaning to be a shooter, which I did. Again, not a rare piece, but a great shooter. I have an engraved Remington-Beals that is worth quite a bit and I only cleaned it with soap and water. To say that cleaning an antique automatically devalues it might be a stretch - it depends on the gun, its rarity, condition, etc.