This is really not available as a true patine. HOWEVER, , where
there is a will, there is a way!!! Get graphite lock lube in a
spray can. It is graphite (black) is a very light media, that keeps
it one the piece). Spray the graphite onto your item, and via a bit
of experimenting, you can figure out when to wipe it off to get what
you want off, and leave what you want on. This was given to me by a
major pewter figurine mfgr. a number of years ago. We struggled with
getting a nice black patina in the recesses, and FINALLY, with this
bit of info. we now have what we are after, ,easily and repeatably.
Hope this helps.
PS There is not material that will give a black patina to pewter, at
least that I have ever found, and I have looked, read, talks and
asked A LOT over many years. Hope this helps you get what you a re