What type of compound should I use?

There are thousands of formulations of compound (concentrated soap) available. The main purpose of a compound is to help keep the process clean. This can aid the process by removing dirt/oil from the parts and to help keep the media clean. Keeping the media clean helps finish the parts because it allows the surface of the media to do it’s job without it “loading” or “glazing” up. Once the media is “loaded” up then it cannot work effectively. The other main feature of compound is sometimes to add a rust protection characteristic to the parts or media.