Coating metal (4)
I believe the answer is:
zinc
'coating metal' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for zinc that I've seen before include "White metallic element, symbol Zn" , "It is used to coat iron against corrosion" , "Metal used in brass" , "Anti-corrosion agent" , "it might be galvanising" .)