I used to use the Tripoli (Red) on heavily oxidized stems but found it's easy to cause damage, or very heavy scratching using it. It will even cause melting if too high a speed buffer is used. I do still use the Tripoli when I'm working on finishing a pipe bowl I'm making as it saves a lot of sanding time.
So I now use sandpaper to remove the worst of the oxidation/green of stems. Once I get the stem black from sanding I then use White Diamond to bring the stem to a glassy shine. I also use the White Diamond on pipe bowls I'm making, as it can save a lot of hand sanding as well.
After that, I apply a coat of carnuba to the stem, which helps keep the oxidation from returning as fast. Remember that when using carnuba, a little goes a very long way.
I use 6" buffing wheels on an aluminum arbor I made myself. Each wheel is mounted to a threaded carriage bolt so that they can be easily changed depending on which I want to use.
You should use a different wheel for each compound or wax that you use and never interchange them. I even have a clean soft wheel I use for a final buff with no compound at all.
While there has been a lot of discussion about the correct speed for buffing and cleaning, I've used a grinder at 3200rpm and now use an electric motor at 1720rpm. If your careful you can use the faster setup and achieve very good results but your techniques will vary just a bit than using a slower motor. No matter what setup you use, practice is the key and cheap, or even trash pipes are good to practice on.
The biggest thing to remember when using a buffer is too do it when there are no distractions and keep a firm hold onto the part/pipe your buffing. I've only lost control of two pipes since beginning to buff pipes, both times ending in disaster for the pipe being worked on.
I wanted to add that I use only the loose sewn wheels and that the more surface area you have the better as it makes working pipes easier.. Some even use the wheels two wide so that they have more working surface area.I've not done this, but lately been thinking of doing just this very thing. You should also keep your wheels clean and free from buildup of compound. There are actually many ways to do this, but I've found that cardboard works very well for myself. I just run it across the surface of the wheel like I'm buffing it. When compound starts to build up on the cardboard, just cut the leading edge off and go back to it.