Added salt of copper — revolutionary! (5)
I believe the answer is:
cured
'added salt' is the definition.
(as in cured meats)
'copper revolutionary' is the wordplay.
'copper' becomes 'Cu' (chemical symbol).
'revolutionary' becomes 'red' (red can informally mean communist).
'cu'+'red'='CURED'
'of' acts as a link.
(Other definitions for cured that I've seen before include "Healed - smoked" , "Rehabilitated" , "Preserved by drying, salting or smoking" , "Mended" , "Healed - preserved" .)