I did that patina with the simplest of methods as a test. I used vinegar and ammonia. I think I buried it in sawdust and poured the liquids on the sawdust, but I am not positive. But first I darkened it a little with Birchwood-Casey M-24.
This time I cast her in two pieces. I poured her head first.
Then her torso.
Not so perfect a casting as her head, but useable.
And she is coming along.
More to come.