Fred, the aqua fortis used on maple is not a problem with respect to metal corrosion later. I have rifle I built about 10 years ago which has shown no sign of corrosion to date. After you heat the wood stained with Aqua Fortis and get the color shift, the wood gets neutralized with baking soda solution (some use ammonia). Not sure that having dissolved all the iron possible in the original solution any significant acid content still present anyway. I have gone to the vinegar/iron lately just because it may be even more authentic. If it fails me I correct it with the alcohol based stains.
