Marker made of carbon material (6)
I believe the answer is:
crayon
'marker' is the definition.
(I've seen this in another clue)
'carbon material' is the wordplay.
I cannot quite understand how this works, but
'carbon' could be 'c' (chemical symbol) and 'c' is present in the answer.
'material' could be 'rayon' (rayon is a kind of material) and 'rayon' is found in the answer.
No letters remain.
This explanation may well be incorrect...
'made of' acts as a link.
Can you help me to learn more?
(Other definitions for crayon that I've seen before include "Stick of coloured wax for drawing (6)" , "Wax colouring stick" , "Source of colour" , "Stick to colour" , "Waxy pencil" .)