Readying antique copper door plates for oil rubbed bronze finish

I've got a number of original copper door face plates from my 1905 house which are in need of refinishing. The majority of the hardware in the house has an oil-rubbed bronze appearance and I'd like to try and match that.

The problem is that the door plates, although copper, appear to have some greyish streaks in them. These streaks appear at the same place on each plate, so I am assuming they are a result of the original method of casting and/or pressing. If I apply liver of sulfur ⇦ on eBay or Amazon [affil link] or another darkening agent, will it darken unevenly? Do I need to do some sort of acid wash or possibly electroplating prior to application of the darkening agent? Will electroplating or washing harm the intricate design on these antique plates?

Any help is much appreciated!

That is job for professional metalwork conservator.Hope it helps and good luck!