However corn cob does in fact polish, it also cleans, just takes longer. I use a grit of corn cob 20/40 grit available from Grainager or their retail/mailorder outlet DrillSpot. From DrillSpot it comes directly to my door freight free for approx 80 cents a lb, and being light weight which corn cob is you get a lot of media in the 40 lb bag.
Econoline 526040G-40 Blast Media, 40 Lbs, Corn Cob, 20/40 Grit
Above is the link for DrillSpot.
.