Pickling the bronze doors for the U.S. Capitol to a dark statuary finish

I'm fabricating the bronze doors for the U.S. Capitol, these doors get a dark statuary finish. I was told there was a pickling solution to aid in the coloring process, along with the darkening agent. If this is true can you tell me what this product is and where I can get it. I'm trying to achieve a more uniform color over the surface of these doors, also having a bit of a hard time getting the acid to react at all on certain pieces. Any help would be great. Thank you

Dear Jon!
Buy yourself one good book on patination of copper and its alloys (Rowe, Hughes book "The Colouring, Bronzing & Patination of Metals" [on eBay, Amazon, AbeBooks affil links] is best on that subject). Good luck!

Dear Jon.
I am a bronze fabricator and finisher what you would want to do is use a product called antique black made by Birchwood Casey. Thanks and good luck Dale