Guys,thanks for the good replies.you all make good points. Next question: What did they do 200+ years ago?[as in nuetralise or not]
They did not have to neutralize if you go by the method described by Calvin Hetrick when he observed one old gunsmith doing it.
The gunsmith reacted the iron in the diluted nitric acid until the acid was almost totally "spent". Observed when the bubbling ceases in the mixture as it is made. The stain solution (ferric nitrate in spent acid) was applied to the stock. The stock then being GENTLY heated over the forge fire. If you heat a ferric nitrate (nitrate of iron) solution above 150 degrees F it will break down giving off the lower oxides of nitrogen. This may be smelled as the stock is being heated. While traces may remain the wood after heating, most of the flashed off lower oxides of nitrogen cannot reform with water to form nitric acid within the wood.
A simple baking soda solution will kill off any traces of the acid or lower oxides of nitrogen in the wood.
As pointed out. True nitrate of iron stain may, or may not, darken considerably with aging. Depends on the concentration of iron in the stain solution applied. An "iron rich" solution will darken considerably within about a 10 year period after the stock is stained. An iron weak solution will not darken nearly as much. Most of the darkening is the result of a slow reaction with any tannic acid in the wood. Some stocks may contain fairly high levels of tannic acid while others have very little.
I would point out that sometimes this slow darkening reaction will bring out curl that was unseen in the stock blank. My test rifle from 1984 was a second that I got cheap. Only a little curl showed. Now it shows all kind of curl and the curl is an intense black color. The so called curl picks up greater amounts of the iron stain, during staining, compared to the areas where the grain is parallel to the surface of the stock.
When gently heating the stock, after staining, and what and how much caustic you use will alter colors with the nitrate of iron stain.
Beware of some of the commercial stains based on one or more acids with "iron added for color". These stains depend on heat to chemically char the wood's surface to produce the color. These MUST be neutralized. One was a mixture of nitric and hydrochloric acids with a small amount of iron added. When you use a live acid and heat to color the wood it may well come back and haunt you later on. The acid(s) get locked in the wood under a finish. They then migrate through the wood and attack metal parts on the gun. As Chuck Dixon once commented, he never saw an original with finish in the lock mortise or in the barrel channel and none had corrosion problems.
