Good quality bone and wood charcoal of the type sold by Brownells and a few other outlets is all you really need to get great colors. Potassium Nitrate is not necessary, but it does add some extra blue, though I can take it or leave it and most folks would never know the difference unless you pointed it out to them. You can use an air line to the tank if you want, I do, but I shut it off before I quench. I believe the main point is to get the oxygen content in the water at a high level, a freshly filled tank doesn't require any further work as there will be plenty of air in it already. I do wrap my parts with soft iron wire and that gives much more consistent results than relying on a stream of bubbles coming up from the bottom of the tank.
Spend some time looking around on the net. There is lots of good info on this topic that has been written. Some of it is good, and others will get you into trouble. Anything Jerry wrote you can take to the bank. I have no experience getting colors with kasenit, but sometime I will try it and see what happens.
