24mm, Civil War Era Georgia coat button, with a "Van Wart Son & Co" backmark.  A raised horizontal line (near the shank) adds an interesting detail to the reverse of this button.  It is part of the original manufacture of the button and seems to be where the craftsman laid down his tool while brazing the shank... or misapplied some brazing and attempted to scrape it up.  It is contemporaneous to the manufacture of the button and the shank is real and unmodified.