Ammonia for me too however, it can not be understated that you need to get the right kind of ammonia. You want something that says Ammonium Hydroxide, most that I have seen are 10%
This is where the danger comes in. If you get the wrong ammonia, anything like perfumes, soaps,colors, or something called surfactants, you are in a world of hurt. Ace hardware is a good source for this ammonia if you have one in your area. If you have any doubts what so ever about the ammonia you want to use, post a picture of the label and ask questions here.
Good luck and have fun!