I'm not quite sure what you mean with oxidation, the white powder that really is Ti oxide if you dry-burn Ti really hard (white glowing coil) or the colors the wire goes through when pulsing it softly?
I clean fresh wire with alcohol before coiling, and dry-burn both new and used
coils to a red-orange glow before wicking. New
coils get a blue-greenish color from that, old
coils will have a light-greyish color afterwards, and I decide by the "darkness" of grey if I want to reuse that coil or go for a new one. I have a relatively heavy used coil that dates back to December, but with a fresh wick it vapes like new.
Uhm, you might guess I'm not concerned at all about discussion about residues on the coil, to dry-burn or not to dry-burn etc..