If your Pyrex dish or bowl has gotten stained with black spots, there is no need to worry. These spots can be removed fairly easily with a few simple steps. First, fill the dish or bowl with hot water and add a tablespoon of baking soda. Allow it to soak for at least an hour. Then, use a soft cloth to scrub the spots until they are gone. Rinse the dish or bowl thoroughly with warm water and dry it off. If the black spots are stubborn and don't come off with this method, you can try using white vinegar instead of baking soda. Fill the dish or bowl with hot water and add 1/2 cup of white vinegar. Soak for at least an hour and then scrub with a soft cloth until the spots are gone. Rinse and dry as before.