...model boilers have been painted with metal flake(or fleck, as you say) to represent Russia Iron.This is TOTALLY BOGUS. People seem to be confusing metallic with metal flake.
As for the DRR engines, I gather their boilers are actually painted. Is the finish metallic, metal flake, or simply high-gloss?
My intention is to model the DRR engines as they appear today. They are somewhat caricatures of historic locomotives. The boilers are painted with what appears to be automotive paint and are highly polished, maybe even waxed. The "metallic", "flake" or "fleck" is the same that you see in many automotive colors. I'm sure that they chose a bluish color on the Holliday and Gurley as a tribute to Russia Iron, but it is not trying to duplicate Russia Iron. The Holliday and Gurley are mostly blue with a hint of green, the Ripley is green, the March is maroonish/magenta red and the Kimball is almost black. All have the added "glitter" sparkle of the metallic fleck. This metallic fleck only occurs at the boilers. the other painted surfaces of the locomotives are high gloss solid colors.
C K Holliday
Ernest S. Marsh