In ye olden times (and in 3rd world countries) tanning a hide to make leather used dung, urine, cow brains etc. and it sounds a bit like the process you have just followed. So perhaps modern tanning techniques would age the brass as well. I found this crowd (with an outlet in Hunstville).
I think it may have been me who mentioned the Imagineers' method of aging brass. I have scoured the Internet, but I have not been able to find any references to the recipe. My vague recollection is that in addition to cow poo it included straw, vinegar, and molasses. I could be wrong abnout the other ingredients- it's been many years since I got the tour of the "underside" of Epcot Center.
I can understand the smells you are talkign about. I do composting of kitchen waste at home so can figure out. Yes cow dung is extremely rich in so many minerals. Dried cowdung is used as fuel in many parts of India. Comingto the aging of brass, the pictures you have put looks like a piece of art. Where are you going to use them...I mean why would you age the brass.