Pane spattered with oil, whitish glass (7)
I believe the answer is:
opaline
'whitish glass' is the definition.
(I've seen this before)
'pane spattered with oil' is the wordplay.
'spattered with' is an anagram indicator.
'pane' anagrammed with 'oil' gives 'OPALINE'.
(Other definitions for opaline that I've seen before include "Like some gemstones" , "not entirely clear" , "white!" , "Opaquish glass; iridescent" , "Milk glass" .)