One component of brass (4)
I believe the answer is:
zinc
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">one component of brass</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for zinc that I've seen before include "Anti-corrosion agent" , "Blue-white metal" , "Metallic element present with copper in brass" , "Type of metal" , "It is used to coat iron against corrosion" .)