We make brass lanterns in a small shop in Japan. A customer asked for a black one, so I went looking for a way to do it.
The obvious answer here is chemical blackening. Temple fittings in Japan have been finished that way for centuries and the color has real depth to it. I almost went with it. Then I picked one up and thought about how our lantern actually gets used. You carry it by the handle, you turn a knob with your fingers, and in oil mode the whole body gets warm. Blackening has almost no thickness. It is the surface itself changing color. Temple fittings survive it because nobody picks them up and walks around with them.
So, plating. And that is where it got interesting for me.
Our body has an oil tank bore, a small gear that opens and closes the air vent, and threads. With electroplating I would get heavy buildup on the outside corners and almost nothing down inside those features. Uneven thickness on a moving fit means either it binds or it rattles. Electroless plating goes on at the same thickness everywhere the liquid reaches, so the internal mechanism stays at the dimension I actually designed.
I ended up picking the finish for the parts nobody is ever going to look at.
One thing I am still not settled on. Do you machine undersize to leave room for plating thickness, or do you hold your dimensions and put a tight tolerance on the plating spec instead? I have been doing the first one, but I would like to know how you handle it.