New Model Remington Question

[raascht]

Looking for some info on this revolver. It is marked at top of barrel "PATENTED SEPT. 14. 1858/ E. REMINGTON & SONS. ILION NEW YORK. U.S.A./ NEW-MODEL" Serial number is in the 117XXX's and it has a cartoush visible on the stock marked "GP"... Small single letter inspection marks "W" are stamped on most components of the piece. My question is on the finish of the pistol... It appears to be nickel but I am nor sure if that was an option in 1864. Could it be silver plated, or maybe nickel plated at a later date? I am including a couple of images that may help... you can see the brass coming through under the silver of the trigger guard.

Any ideas or info. would be greatly appreciated.

Thanks much!