There are two main reasons to blue a gun using hot rust bluing over commercial immersion bluing, That is because the ribs are soft soldered on the firearm (seen in older firearms and some newer very high value guns.) and also because it gives you a richer royal blue. Here are some pictures of a barrel I recently hot rust blued, This is a very durable and traditional blue. It is also very labour intensive and so is more expensive to do.
This is the type of finish often found on weapons of great craftsmanship such as Purdey shotguns etc. We are very proud of our bluing prowess and this is an example of an older shotgun blued in an old world manner, After we complete the bluing process while the barrels are still piping hot we give it an in the steel linseed oil finish, The pores in the steel absorbs the linseed oil making the water resistance of this blue particularly good. We keep rubbing it down until it will absorb more and then put a coating of a modern gun grease, We believe this gives the best of both the new and old world technology’s.