Become rusty (7)
(Other definitions for oxidise that I've seen before include "Combine chemically with a particular gas - ie six do (anag)" , "Eg, go rusty" , "Eg, rust (S, not Z)" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">become rusty</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>