Ok here goes .
Browning does not have to take a lot of time . What takes time is producing that nice brown on steel vs. iron .
When today’s steels rust , it’s the Iron level in that steel beginning to corrode/ build iron oxide . The lower that level of iron , the longer the process to produce a good quality brown.
Case in point , even here in the area I live in which is very low humidity , I can lay up a coat of rust on an Iron barrel in just a couple hours , using nothing but a humidity box and water . Doing so I can produce on iron , at minimum 3 good rust and card cycles a day .
Now if I stimulate that rusting with a surface application “BRONZING” I can get very near to a rust cycle every hour . In fact even without a damp box , urine will produce , in this low humidity environment , a very heavy rusting even on steel , in one day or a fine rust layer in a mater of hours . No to mention the stronger the urine , the faster the rust will build especially when applied to bare iron or steel .
Thus , while a fine rust is what were after , you can then produce multiple rusting and carding cycles in a day even on steel . more so howvere on iron , for if you dont , you can easly end up with a great degree of pitting on the serface . which IMO is undesirable .
Now with that being said , have you ever noticed what happens when you get AQUAFORTIS on steel and especially iron and then hit it with heat ?
what you saw was called Bronzing Harrison mentions it in his writings in 1883
“There is another material sometimes used , which is butter or chloride of antimony. Its sometimes call browning or bronzing salt. When using this substance a mixture is made with it and olive oil . This is rubbed on a barrel that is slightly heated , and is then exposed to the air until the required degree of browning is arrived at. The operation of the antimony is quickened by rubbing after it , a little aquafortis .”
sound familure ?
My point is that there are thousands of different recipes for “quickening” all that work very well and relatively faster on iron then what we see commonly used of steel barrels today .
Ok so lets look at rust black or rust blue . The process to convert red iron oxide to black iron oxide takes 2 things .
1)heat
2) H2O or more correctly oxygen and hydrogen in the presence of heat
Manufactures for centuries have built on that simple conversion to the point that the vast majority of what we think today as being chemical blues were or are ,in fact not .
Winchester blue , Remington blue , Ithica and Colt black , were all rusting .
Makers like Purdy , Pauly , Parker , Greener , Richards , Fox ……… all got their fine finishes from a process of converting red iron oxide to black iron oxide and in the process producing the black staining rust which gives a very deep and dark color .
The process can be as simple as heating a browned barrel to a point where water will boil , then quenching it or wiping it down repeatedly as with a cold brown OR as long an drawn out as the process used by Purdy Parker or Greener or as extravagantly detailed and complicated as the process used by the likes of Winchester, Remington or Colt .
But if you truly want to know what would have been done for your gun , you need to research the time and place it fits in as well as the person would have most lily made it. As I said before . Here in the states , you don’t read much on browning being offered until the later part of the 18th century .more commonly early in the 19th century .
Prior to that you had barrels in the bright or in the blue . IE Grey colors or blues ranging from fire blue to rust bluing . Both of which are very quickly produced on Iron .
having a barrel in the bright also doesnt mean rust . if care is aken to prep the barrel correctly and then maintain it , you should have very little rusting at all as can be attested by the numbers of original pieces which even today have a very wonderful grey color and patena with little to no rusting