The parts for 622 received a coat of old Polly Scale steam power black, and despite the love-hate relationship I maintain with my old Pasche, it went mostly okay. The one part that came out strangely is the tender tank. This turned out with something akin to a salt stain. My best guess is it was residue from the decal setting solution I used with the rivets.
It was barely visible, and maybe I would have gotten away with it on the layout. However, maybe I wouldn’t have too. Ultimately, I decided to partially strip the tank and redo it.