Fill a small microwave safe bowl with 1 cup of apple cider vinegar. Warm the apple cider vinegar in the microwave for 30 to 45 seconds on the highest heat setting.
Remove the apple cider vinegar from the microwave. Pour it into the bakeware with the gray film in it.
Add 2 tablespoons of white sugar to the apple cider vinegar. Stir the sugar into the warmed vinegar with a wooden spoon until dissolved. Allow the warmed vinegar and sugar mixture to remain in your baking pan until cooled.
Scrub the inside of the baking pan with a nylon mesh sponge, and with the vinegar and sugar mixture to remove the gray film. Rinse the pan with warm water.
Tackle any remaining gray film and stains by sprinkling baking soda over the damp sponge. Scrub the metal bakeware to remove the last of the stains.
Clean the pan with warm water and two or three drops of dishwashing detergent on the nylon mesh sponge. Rinse the pan well to remove soap residue. Dry the pan with a clean, kitchen towel.