Cinders put on diamonds showing sparkle (4)
I believe the answer is:
dash
'sparkle' is the definition.
(thesaurus)
'cinders put on diamonds' is the wordplay.
'cinders' becomes 'ash' (I've seen this before).
'put on' is a charade indicator (letters next to each other).
'diamonds' becomes 'd' (abbreviation for the card suit diamonds).
'ash' put after 'd' is 'DASH'.
'showing' is the link.
(Other definitions for dash that I've seen before include "Hurry; hyphen" , "Run hurriedly; hyphen" , "Striking" , "Daring" , "Short fast run" .)