Here's a good list of the Brit proof marks which may come in useful.


http://www.hallowellco.com/british_proof%20marks%20-%20syntax%20by%20date.htm

Good info from Tim too.
I'm really not an expert on the history of blacking/browning but I believe some brit makers sold guns black and white patterned barrels yet it seems to be the 'proper' way was browning. I think either can look stunning and while I've not been asked to do a black and white set, I'd love to do some.
Perhaps Drew could comment on this, he's a mine of information on this subject.
Joseph Asbury was one of the well respected Birmingham action maker. There's a few mentions of him on this site, may be worth a search. I'd post links but I'm hopeless with the computer side of things. I've found pics of the fields gun I looked at too but cannot get my photobucket to take orders from me smile I'll see if I can post the link instead. Sadly, I've not found the pics of the flats on the one I saw.

Rust never sleeps !