Dewey, I beg to differ with you. I refer you to page 428 in John Houchins' new book,"The L.C. Smith trigger guards are among the most beautiful of all the classic guns. The Hunter Arms Co used a process known as 'Niter Blue', a process originally developed by the Springfield Armory." From the same reference, same page, the frame and lockplates were casehardened. Carbonia blue seems to have been used mainly by the Colt Patent Firearms Co., but I'll defer to Ken Hurst who was there as one of their Master Engravers. Best, Dr. Bill