My MTBs from Canfield Bikes have typically been raw - currently on a raw tilt. One of them was a limited edition polished:
https://nsmb.com/articles/canfield-b...nce-le-review/
I've stripped smaller parts before, without any clear they've oxidized. Had a friend that works in auto so he cleared coated them for me.
Otherwise there's this:
https://www.kbs-coatings.com/diamond...r-aerosol.html