Hey There Hi There Ho There
A little information here. The "Old Silver" finish is also present on the "Marshal" 1851 44s, and the Capt. Schaeffer replica and now several other(s). The finish is actually highly polished steel that is then heat treated. At least, that is my understanding. There was, at one time a misconception those guns were Stainless ... NOT. And they WILL rust if not cared for properly.
I currently shoot a whole pile of the Pietta guns of that "Finish" and really like 'em.
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PS: RE: THE GRIPS. Recent built (last couple years) of Pietta 1851 replicas now sport a grip of more Colt portions. The old "Trombone Bell" grip are GONE!!