I have a couple of 1937 Brazilian Contract M1917 revolvers with a strange, matte, dark gray finish. You can see it's fairly thick where it partly fills in the Brazil stamp. The two screws furthest from the trigger appear to have the same coating. The other two screws and the thumb piece are more like I'd expect from a factory blue finish. Can anyone tell me if there's any way this came from the factory, or maybe it was something commonly done by Brazil. And does this affect the gun's value? I have a few I'm planning to sell. Thanks in advance.