Egg found inside platinum vessel (3)
I believe the answer is:
pot
'vessel' is the definition.
(pot is a kind of vessel)
'egg found inside platinum' is the wordplay.
'egg' becomes 'o' (I've seen this in other clues).
'found inside' is an insertion indicator.
'platinum' becomes 'pt' (chemical symbol).
'o' placed inside 'pt' is 'POT'.
(Other definitions for pot that I've seen before include "Somewhere to go" , "Cooking vessel or slang marijuana" , "...Karenina(Tolstoy)" , "Plant holder" , "It may call the kettle black" .)