To add a bit to what Norris wrote.
In the 70's her in Southern California, Art Stump while not known to build many, most it seemed were "black chrome" in early 1973 I asked him what he did as his was fully polished everywhere and of consistent color.
Art stated he used Highland Plating, a firm still in business, probably the premiere plater in Los Angeles who does aerospace to art plating. Art further advised he did all the polishing himself, which in seeing his shop I do not doubt, and assisted in the anode placement to get the finish into the tight spots. He did not elaborate on that, but I bet he made some fixtures and or racks for him /them.
Even back then a top notch chrome plate job from Highland was not cheap, $200.
John Jorgensen
Palos Verdes Ca USA