Still looking for photos. I have bought 4 dif rifles in the past that were stained almost Black finish. Removed the finish & you would not believe the striped wood that was hidden under that black aquafortis finish. That is why I don't use aquafortis. (called Stink Water in the old days) 50 yrs from now it will be black & just another ole useless flintlock shoved in the back of a closet & nobody appreciate what a beautiful piece of wood it really is.
Oh it initially looks awesome, but it slowly goes to black.
Bill Knight told me of this blackening of the stocks and I started using the store bought stuff I had as barrel brown when mixed with the same companies cold brown. Worked great when rust bluing 4140 and 1137.
Shop made ferric nitrate does not do this. But the commercial stuff is often adulterated with hydrochloric and it WILL darken a stock over time. Below is a curly maple horn base plug done over 24 years a ago with stuff I got from TOW, its near black, its looks darker in real life. I have rifles about 20 years old stained with actual ferric nitrate made from only nitric acid and water with some iron/steel added and they look just like then did when I finished them.
The reason original rifles are very dark in many cases is due to the linseed oilk based finish being blackened by sulfur dioxide and other contaminates resulting from wide spread used of coal in the East from heating and industry. It will react with the varnish and turn it black. This has nothing to do with the stain or the color of the original finish.
The reason that some (maybe all) commercial “aquar-fortis” stains are made with AQUA REGINA, Nitric and Hydrochloric mixed, is that its more aggressive and will dissolve to iron/steel faster or so Bill told me. This is mix was “Regal water” because it will attack gold. IIRC.
This rifle has been hunted with in good weather and bad and has been shot in many matches I have not done anything to it since the last coat of oil about 20 years ago. But it does show some lightening in the wear areas Looking at the forend I may put a little finish on it. The buttstock is from another piece of wood and its darker in some places. “Someone” screwed up the first buttstock.
I never tired dilute nitric acid on a stock. Seems to me this would need some serious neutralization. And the stuff I was given about 20 odd years ago by a guy who gave up gun work is REALLY active stuff and I would wonder how far to reduce it to make it suitable, or even safe, to put on a stock. Reduced 50% it will still boil vigorously when nails or such are added to it.
