The floor plate seems to be the weak link in the blueing process(es).
Rust blueing for barrels, Machine (charcoal or carbonum) blueing for frames, trigger plate and trigger guard. Small parts were niter blued.
As Mr. Murphy stated, it's a pretty good indicator that the the metal finishes are original.
IMHO, with only 30,000 of these fine doubles produced, far too many have been ruined by the likes of CSMC
in their attempt to whiz and transform them into "like brand new and virtually unfired" guns. Philistines!
An admirable, original condition, pre war 16 gauge Vent Rib Trap Grade Skeet (G2155B)
whose checkered butt has not been "erased" with a red pad.
Andy...exactly!