Iron nitrate is a favored stain for maple gunstocks. It imparts a traditional, durable, and beautifully rich color.
Directions: Apply to wood. Allow to dry. I usually wait for at least a half hour before applying the heat. Overnight is fine. Heat until color changes to reddish brown. While heating, concentrate on one particular spot with only a bit of movement of the heat gun. When it gets hot enough, it will turn to an orange brown color. Then just start moving the heat gun slowly along to heat more of the stock. The only thing to really watch for is to not overheat corners. They will char and turn brown or black. Start in more open areas to get the feel. The only thing to stress is that you must heat it pretty hot to get the transformation. The color change will be pretty dramatic, so don't stop heating until you see this occur.Reapply if needed. Apply finish of choice.
FAQ for Iron Nitrate:
Do you neutralize? I don't neutralize my iron nitrate (aqafortis). I do, however, keep it out of inlets. It can cause some slight rusting and you never see it in inlets of original work. There's nothing wrong with neutralizing with baking soda either, though. Sometimes it's good to rub out the stain a bit. My advice would be to just experiment. If you have some scraps that will help.
What if the color is a little green? You are probably not heating the stock enough. You should see it change to a brown orange color when it's properly heated. It's a bit scary, but without enough heat you won't get the proper color. The only thing you have to be careful about is not overheating corners of the stock. It heated to much you can scorch them. Practice on a piece of scrap if you have some.