At the end of Bands of Mourning when Wax sees the vision of Kelsier with a spike in his eyes like the statue.
It has been confirmed that Kelsier is the Sovereign If I recall correctly.
He could be using Ferurchemy due to the spike but we don't actually know how the Bands were made and what Kesier has been doing and how he knows and is doing what he is doing if that makes sense.
I hope this makes sense