Brass or bronze (5)
I believe the answer is:
alloy
I believe this is a double definition.
'brass' is the first definition.
(I've seen this in another clue)
'bronze' is the second definition.
(thesaurus)
(Other definitions for alloy that I've seen before include "Mixed metal" , "Mixture of two or more metals" , "Devalue" , "Metals fused together" , "A mix of two or more metals" .)