Microwaves are built to be durable and sturdy, but they aren't invincible. Just one burned bag of popcorn or overcooked plate of leftovers and your microwave could be covered in a thick, black film that is nearly impossible to get off. Although you may feel like throwing in the towel and buying a new microwave, there are a few ways to get your old, scorched microwave oven looking brand-new.
Erasing Sponge and Bleach
Purchase an erasing sponge, like Mr. Clean Magic Eraser, at your local drugstore or grocery store. Wet the sponge slightly and rub the sponge against the walls of the microwave. It may take a lot of scrubbing, but the scorching will lighten slightly.
Next, take a paper towel and soak it in bleach. Carefully wring the paper towel out and stick it to one side of the microwave. Repeat three more times with three more paper towels to cover each side of the microwave, as well as two for the ceiling and floor of the microwave, if necessary. Leave the paper towels on for several hours, or overnight, depending on the severity of the scorches. Remove the paper towels and scrub with the erasing sponge again, which should remove the scorches completely.
If the above solution does not work to completely address the scorch marks, use vinegar on the remaining stains. Place a large bowl of white vinegar in the microwave and allow it to boil for five minutes. Remove the bowl of vinegar and dip an old toothbrush into the bowl, then dip the toothbrush in table salt. Use the toothbrush to scrub and loosen the stains from the walls of the microwave.