Hi Red Owl,
The best way to make curl "pop" really is a matter of personal preference and objectives. If a nitric acid-based (aqua fortis) or acetic acid-based (vinegar) stain gives you the color and curl you like, they are probably the hands-down best stains to use because they actually oxidize the wood rather than stain it. That means they never fade and they generally highlight curl very vividly. However, in my experience, they are $#@*-shoots with respect to color and often do not meet my needs for achieving my objectives. They also tend to be boringly monochromatic when used alone. I can control color and achieve a deep polychromatic effect readily with aniline dyes, however, they can fade if left in bright sunlight over time. Nonetheless, I've had good luck with them over 30 years. My preferred method for curly maple is to paint the wood with dilute nitric acid (not aqua fortis or ferric nitrate, no iron in the mix), let dry, and blanch with heat. It will usually turn a soft orangy-pink color. I neutralize acid in the wood with a baking soda or some alkaline solution. Then I paint the stock with brown-colored dyes or stains. I usually use aniline dyes for this. The acid gives the wood a deep reddish undertone that highlights the curl and the dyes add darker color without obscuring the reddish undertone. There are stains that you can use to paint over the nitric acid and achieve beautiful results as well but you want to experiment to make sure they don't obscure the grain with actual pigment. I currently live in a place where getting pure nitric acid is difficult and expensive. Therefore, I use red aniline dyes on maple to get the red undertone, however, I would rather use the dilute nitric acid. You can get aniline dyes from Brownells as well as most good woodworking stores (Lee Valley, Woodcraft etc.) I believe Moser is one company that makes oil, alcohol, and water soluable aniline dyes.
Keep in mind, water-based dyes or stains (all the acid stains are water based) raise the grain of the wood, which has to be whiskered. That is not a problem for unadorned guns but can be an issue if you have lots of relief carving. If that is the case, you might want to consider oil or alcohol-based dyes or stains. I still use water-based colors on my carved guns but I very carefully clean up any whiskered wood in the carved areas with razor sharp knives or scapers.
dave
