The red junk will rub off on your brass, leaving a film behind. It's usually made by Lyman, called tuff-nut. Quite simply, you don't NEED anything on either walnut or corncob to CLEAN your brass. If you want a high shine, you'll have to add some sort of tumbler polish additive. They make one that's green as well

Flitz makes one, Midway makes another, Berry's, dillon too. What works well, is inexpensive is nu-finish car polish. It has some mild abrasive, AND a tiny bit of wax remains on the brass. This is important to preserve the shine, and prevent brass tarnish.