Steve, you're absolutely right that many rust bluing solutions contain copper sulphate. And I've also heard that you can detect a cold blue touch up by sniffing or even tasting?? for the copper due to the copper sulphate in most cold blues. P.S. I don't know how I missed the fact that you have a new (2007) book, "Double Guns and Custom Gunsmithing", but I will make room for a copy in my library. Keith

Voting for anti-gun Democrats is dumber than giving treats to a dog that shits on a Persian Rug