I don't think that fits, given that tin overcharges a savants senses when burned, and leaves them without senses when not burning I would imagine that a Copper savent would when burning be immune to all forms of magical detection, even those not geared towards sensing magic, while when not burning copper, bronze or other investiture detection would pick up on their souls.
I think that feruchemical duralumin is closer to what you are thinking.