Can you explain the difference between libun kal and libun gamur and when libun gamur is required?
The Shulchan Aruch only mentions one type of libun and that is when the metal heats up to the point where sparks fly. The Rema mentions an idea of a more lenient type of libun for things that usually need hagala (dipping in boiling water) whereby the metal gets heated to the point that straw will burn when touching it.
In reality, it comes down to how the pot or pan is used. If it is used without liquid, then it requires heating up the pot on the highest flame that the pot or pan is used or throw it in the oven on highest setting for a few minutes.
All this only applies for koshering for Pesach. The rules are a little more complicated for issur veheter
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