My friend accidentally turned on a burner that had a plastic shopping bag sitting on it (older Frigidaire cooktop). He caught it quickly, but it left a residue on the coil that he hasn't been able to remove with a scrubber or even a pumice stone. Trying to burn it off using the High setting didn't even faze it. If pumice didn't work, I tend to think steel wool won't either. Any suggestions on other methods to try?

