Yes the media gets dirty but the dirt is retained by the media. I use ground corn cob media and Brasso. I keep a "wet" batch with the Brasso on it and a "dry" batch for the final polishing. When the wet batch gets too dirty I pitch it and use the dry batch with the Brasso. You can buy ground corn cob in 50 pound bags.Cant the walnut or corn media get used and dirty ? There by adding a fine powder residue to the "clean" cases ?