Jelly seen in Mantegna's pictures (5)
I believe the answer is:
aspic
'jelly' is the definition.
(I know that aspic is a type of jelly)
'in mantegna's pictures' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ASPIC' can be found hidden inside 'mantegnas pictures'.
'seen' is the link.
(Other definitions for aspic that I've seen before include "Savoury jelly for meat or vegetable" , "that's clear?" , "Clear meat or fish jelly" , "Preservative jelly" , "Stock set with food" .)