Here's a related one for you....I stained a stock with ferric nitrate in ethanol. No acid used at all. Neutralized it anyway with baking soda and water...twice... and dried the stock well before the finish was applied. Even put a thinned coat of the finish in the lock mortice, barrel channel, under the butt plate, patch box, and in all the inlet areas. About a month after the rifle was done, I noticed the patch box spring was rusted. I pulled the lock and it also had a lot of fine, red, internal rust. So did the lock bolts and the trigger and some on the barrel. Cleaned everything up, everything got a thin wipe down with CLP and put the rifle back together. A month later the same thing. I still haven't figured it out.