Artist on that material (5)
I believe the answer is:
rayon
'material' is the definition.
(type of fabric)
'artist on that' is the wordplay.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'that' becomes 'yon' (archaic term meaning 'that').
'ra'+'yon'='RAYON'
(Other definitions for rayon that I've seen before include "Man-made fabric" , "Synthetic material" , "Semi-synthetic material" , "Imitation silk" , "Artificial fibre" .)