Mate's porcelain (5)
I believe the answer is:
china
I believe this is a double definition.
'mate's' is the first definition.
(cockney rhyming slang, mate is china plate)
'porcelain' is the second definition.
(I know that china is a type of porcelain)
(Other definitions for china that I've seen before include "World's most populous country" , "It's fragile, though its economy is not!" , "set of porcelain" , "Ceramics; country" , "porcelain cups?" .)