Making better copper band (6)
I believe the answer is:
curing
'making better' is the definition.
(I've seen this in another clue)
'copper band' is the wordplay.
'copper' becomes 'Cu' (chemical symbol).
'band' becomes 'ring' (a ring is a band of metal).
'cu'+'ring'='CURING'
(Other definitions for curing that I've seen before include "Preserving fish, meat, etc" , "Making better" , "Preserving, fish perhaps, by salting etc." , "Smoking" , "Preserving meat or making well again" .)