I could use some help using a cast-iron grill pan with an induction cooktop. I have a Lodge square one, for one burner, and the Lodge two-burner reversible grill/griddle. Both will heat up fine on induction. My problem is that when the griddle gets really hot,it develops a black residue, which I believe is carbonization. This happens with both pans. I'm still not sure what to do with the pan at this point. Or whether the pan is not seasoned enough yet to use such high heat