Teacher's favourites covering clear iodine with hot piece of lab equipment (5,4)
I believe the answer is:
petri dish
But I can't explain it at all! Could you help me understand?
(Other definitions for petri dish that I've seen before include "Type of plate used for culturing bacteria etc" , "Shallow plate for lab study" , "Container for growing cultures" , "Shallow bowl used to culture bacteria -- priest hid (anag)" .)