Traveller involved primarily in china and metal (8)
I believe the answer is:
chromium
'metal' is the definition.
(I know that chromium is a type of metal)
'traveller involved primarily in china' is the wordplay.
'traveller' becomes 'rom' (individual belonging to the Romani people).
'primarily' says to take the initial letters.
'in' indicates putting letters inside.
'china' becomes 'chum' (china plate is Cockney rhyming slang for mate).
The initial letter of 'involved' is 'i'.
'rom'+'i'='romi'
'romi' placed into 'chum' is 'CHROMIUM'.
'and' acts as a link.
(Other definitions for chromium that I've seen before include "Chemical element" , "Metallic element used as protective coating for other metals" , "Hard brittle metallic element resistant to tarnishing" , "Metal used for plating" , "Metal, symbol Cr" .)