Brazing on gun won't darken to match the iron barrel

Hi
I weld a part of my gun barrel with brass and I oxidize the barrel, but the brass doesn't turn black. Is there any way to oxidize the brass? if possible a formula to turn black brass and iron to a consistent color in the entire barrel?

Thanks very much

Oil your object very, very slightly and then heat it slowly to max.400 C.According to old books boiled linseed oil ⇦ on eBay or Amazon [affil link] is best but you can use any edible oil or fat,or even 20% shellac solution(first try that process on some iron scrap!).Hope it helps and good luck!

I have done this with olive oil on an aluminum pistol frame. It actually bakes the oil and leaves a hard black coating. Make sure you have plenty of ventilation, it sure does stink.