I would just like to add a few things that my post did not make very clear. Firstly about the rust bluing process the people who were undertaking this where doing it to earn a wage so their outlook was more along the lines of speed and only wanting do the work once. So more often than not they were using express rust bluing formulas each set of barrels took approximately half an hour from start of bluing to finish, though they did sometimes use formulas not containing mercury and only very low levels of acid to give that blue with a mirror type gloss though taking more time to complete and costing the customer more. Now express formulas had vast amounts of Mercuric Chloride in their makeup so it was inevitable that some would find its way in to the boiling tanks, now Mercuric Chloride did not get the name Corrosive Sublimate for nothing and as they say prevention is far better than a cure because if you do get it in a gun bore it can cause rusting days and sometimes weeks after the work was completed. The bores of the barrels where plugged to keep this out as well as any residual oil in, and if you are processing may be dozen barrels a day the boiling water was probably a strong chemical soup by the days end. Also the pitch in the shellac was there as an aid to its removal no black all traces of it is removed and why clean the bore if there is no need to, so keep as much foreign matter out as possible.
Just a couple of things now rust under the ribs in the barrels initial manufacture especially the top makers here still use the traditional Colophony (Tree Resin) as a flux the reason is twofold firstly to aid the solder to flow at lower temperatures and second it would cover a considerable amount of the bare metal surfaces under the barrels ribs slowing down under rib rusting. And finally after bluing was complete the barrels were put in to a form of dewatering oil based on Lanolin if while re-bluing there where noticeable air bubbles emanating from a barrels ribs these barrels where placed in a hot cupboard for a time, then placed in to a cold dewatering tank and as they cooled down the oil would be drawn under the ribs. The barrels were removed from the dewatering tank and left to drip dry then given a polish with a leather pad improving the surface gloss.
