Very likely no relationship between Darlow and Tobin. I'd say the Darlow gun shown predates Tobin by many years. Actually after the turn of the century, say 1910 or so, the black receiver finish was quite common and in style. Tobin, Baker, etc used it here and many companies used it in Europe for their missnamed Funeral Guns. There is a good article on this black finish by Doug Tate in SSM a year or two ago.

http://www.bakercollectors.com/