Cleaner fuel for artistic medium (8)
I believe the answer is:
charcoal
'artistic medium' is the definition.
(I know that charcoal is a type of artistic medium)
'cleaner fuel' is the wordplay.
'cleaner' becomes 'char' (charwoman is a type of cleaner).
'fuel' becomes 'coal' (coal is a kind of fuel).
'char'+'coal'='CHARCOAL'
'for' acts as a link.
(Other definitions for charcoal that I've seen before include "Fuel - stick for drawing" , "Dark grey colour" , "Sort of grey" , "Art material and fuel" , "Carbonised wood" .)