Grey alloy (6)
I believe the answer is:
pewter
'grey alloy' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for pewter that I've seen before include "Beer-tankard alloy" , "prize-money" , "Alloy used for utensils" , "Tin alloy used to make plates and mugs" , "Alloy of tin and lead, often in beer mug" .)