I first encountered this terminology when I took an 1887 L.C.Smith to be proof tested in Birmingham. Mr Terry O'Donnell who prepped the gun suggested Best Birmingham Brown for a finish.Later that year (1990) I came across a copy of Mr. Angiers Book on gun finishes.In the chapter Finishing solutions with two metallic salts he lists both BB Black & BB Brown.
I assumed it would be relatively easy to replicate and sometime later when back in the states set about collecting all the necessary equipment and supplies to try this out.
The first issue was the Sweet Spirit of Nitre. Apparently commonly used as a cold remedy this was banned by the FDA in 1980 for over the counter sales. I suspect that its initial inclusion was a means to increase the alcohol content in the solution without having to pay the heavy alcohol tax in the UK. In working with the solution I came to the conclusion that the presence of the Alcohol is to speed the evaporation of the solution when applied to prevent puddling, by reducing the evap point it readily spreads on the bbls that have just come out of the boiling water and evaporates very quickly.
Second issue was the Nitric acid Listed as density 1.46 in Angier (concentrated) in the US the commercially available is a much weaker 20% WV solution. per my vendor Spectrum chemical
it is necessary to use 4.2 x the amount 20%WV to obtain the same mole count in the final solution.
The alcohol listed in Angier was 90deg (45%) Avail US was 190
(97%) I used half the mass given in the original recipe.
Both Copper sulphate and Ferric Chloride29% we supposedly inter changeable.
Having got everything together I proceed to start testing.
The results were mediocre.After several attempts I decided to check the mixing Flask It took 125 gms of water to fill to the 100ml line I'd been using!! I ended up re calibrating a couple of flasks to accurately reflect 100 & 200ml volumes. Having got that glitch out of the way I proceeded with repeat tests. Improvement but not good enough.
Then followed a period of searching for improved "Blackness"
To cut a long story short Angier states that he used 29% FeCl3 solution by default as this was the standard strength in both the US and Continental Europe.England never used 29% but used a 44% solution which was later dropped to a 40% solution.
I had my son calculate a revised mole count to match a 40% solution and he came up with a multiplier of 1.22 gms 29% = 1gm 40%.
From this revised formula I started to get good results which when coupled with best practices in cleaning,polishing gave overall very satisfactory finishes.
The revised formula utilizing US commercially available supplies
Copper sulfate crystals reagent quality 2.8gms
Ferric Chloride 29% Sol. 10.0gms
Nitric acid 20% WV 11.75gms
Alcohol 190 proof 1.53 gms
Water Sufficient to make up to 100ml
