Re: Hot Bluing
It sounds like some confusion here. Belgian Blue is rust blue or at least one version of it. Prior to the invention of caustic salt (hot tank) bluing in the mid-1930's, there were hundreds of formulae for rust bluing, plus of course charcoal bluing, Carbonia bluing, heat bluing, temper bluing, etc. Each gunshop had its own mixture, and every book or article on gunsmithing had one or more concoctions, almost like "The Joy of Bluing." Some gave a real blue, others a black, others a brown, still others a plum color. And each had its devotees, insistent that his brew was best.
So it is not a matter of hot tank blue vs rust blue - there are other choices, but most of the others are either variations of rust blue and require the same amount of work, or are not practical today in a small shop.