Science Questions

Why do metal pots spark in the microwave?

I accidentally put a cast iron le crueset pot in my microwave oven for 20 seconds, It flashed - nothing cracked and there was a burning smell. My question is - would it have contaminated the food in the pot? Sharon, Australia

I guess the cast iron pot had a cast iron lid as well.  Microwaves cause electric currents to flow through metal, so you would get a current flowing through both the pot and the lid.  If the pot and the lid were insulated from each other, and there was enough voltage, you would get a spark as the current jumped between the pot and the lid.  This would explain the flash, and it may have damaged the enamel on the surface.  The spark is incredibly hot, and so this could have vapourized some of the enamel, which may be the cause of the smell.

It's unlikely that cookware manufacturers use anything too toxic in the enamel, as you may scrub bits loose and they could wind up in the food.  So although there may have been some enamel in the food, it should be relatively safe and in such tiny quantities that the food would not have been dangerous.

September 2007