How your local blacksmith made them (before the advent of the wire nail manufacturing in the early 1830s).
Heat bar in fire to orange red. Taper bar to shape (1). Partially cut through at length desired (2). Place in nail header (3)(4) and shape head with a good blow or two. Rosebud heads require 4 blows.
Alex W. Bealer; The Art of Blacksmithing, Funk and Wagnalls, 1969