Rust Patina

[cdjordjievski]

Recently I was at some art festival and I saw this lady displaying ceramics with e very nice rust patina. I asked her about the source but all she would tell me was that it was liquid and she applied it with a brush but would not reveal where she got it. I am working on wooden structures covered with bondo and got some nice patinas from sculpt nouveau but always looking for new interesting finishes.
Is anyone familiar with good rust patina for bond or hydro stone (from the gypsum family) preferable friendly to the environment and hopefully me?
Thanks