The finer the polish, the longer it will stay bright. The coarser the polish, the faster it will color. Just like browning or blueing a barrel. If the finish is too fine, it won't take color as well. Daryl's brother Taylor has a 10g bess that he built for himself several years ago and he put an ultra polish on the barrel. After useing it for several years rain and shine, it just wouldn't rust. Still looked just as shiney as the day he built it. He has since browned it. I think he got tired of waiting for it to color naturally.
Cody