Cold blues are basically metal stains, and don't wear very well; I think they are a waste of time. Rust bluing is not hard, but does consume some time. I use Laurel Mountain Forge Browning solution--they have directions to use the solution to rust blue as well as brown barrels. Follow their directions to the letter. If you don't want to spend money on a tank to boil the barrel in, check youtube on how to steam barrels. It works just as well and doesn't cost much for the setup. ( boiling/steaming converts the red rust to black rust, if you didn't know.)