A shiny paint -- English celebrity put on litres (6)
I believe the answer is:
enamel
'a shiny paint' is the definition.
(I've seen this in another clue)
'english celebrity put on litres' is the wordplay.
'english' becomes 'E' (abbreviation).
'celebrity' becomes 'name' (as in a 'big name').
'put on' says to put letters next to each other (some letters go on or after others).
'litres' becomes 'l' (abbreviation).
'e'+'name'+'l'='ENAMEL'
(Other definitions for enamel that I've seen before include "Glassy substance" , "Tooth surface" , "Crown Protector?" , "Decorative or protective covering on metal or glass." , "Decorative inlay" .)