Michael,
There's a variety of ways to add a patina to a stock, and like you said, some folks do it a little better than others. I really feel this aspect of gun building is an art form in itself. And, you'll get the inevitable "let time age it naturally", or some such quote.
At the end of the day, I look at stock patina as a way to show depth and character in a piece of wood. Recessed areas around carving, the lock and side plate, the hollow of a the comb, etc., are darkened. High parts on carving, the edges of panels, the wrist, etc., are lightened. Take a look at guns you like that have been "aged", and ask yourself why that appeals to you. That doesn't speak to the technique, but it will give you a guide for what you want to accomplish. There needs to be a "meathod to the madness", a "road map" for you to follow.
Having said all that, which I think is just as important as the "how to", I'll talk about one technique that has worked well. After the stock has been sealed (I use Permalyn Sealer), let it sit for a good 24 hours. Areas that I want darkened are given a VERY LIGHT application of Permalyn sealer. Just the very tip of your finger will do, and spread it around the area you want to treat. Again, less is better. I then use my finger to rub lamp black into that area. Make sure you get all the recessed areas covered well. After that, use a fine scotch brite pad, fine steel wool, or rag to get the black off the high spots. Again, I think you'll have better results with less sealer. After the entire stock has been done to your satisfaction, WIPE another coat of sealer on the stock. Don't rub it or use a brush, I find a 2"x2" cleaning patch works well. This application will "lock" the lamp black in place. Again, let the stock dry for at least several hours. If areas need it, you can "feather" the edges of the lamp black with fine steel wool, or fine scotch brite pad. You don't want hard edges... After this, add a couple more applications of sealer by wiping on until you get the desired coverage. For me it's usually another two. After the last coat is completely dry, you can rub back with fine steel wool, or fine scotch brite pad if you desire a less than shiny, or duller finish. Since the lamp black is locked into the finish, you shouldn't have any issues with rubbing it out of the sealer.
There are certainly other methods that work very well also, tints, and glazes for example. Experiment and have fun! it's one of my favorite aspects of building a gun.
Ed
