Hi Charlotte. To remove utensil marks and baked on food and grease, make a thick paste with baking soda and water. Spread the paste on the Corning Ware especially on any marks. Use a non-abrasive sponge and scrub the paste until the marks disappear.
Hi Charlotte, here's a lovely tutorial that will show you how to restore the finish on Corningware - https://www.timescolonist.com/reena-nerbas-how-to-restore-stained-corningware-dishes-1.20726091
Here's a link to help you:
Add 1/4 cup white vinegar and 1 teaspoon hand dishwashing liquid to the hot water in the dishpan. Scrub the Corning Ware with a dish scrubber to remove the stains loosened by the oven cleaner. Rinse well to remove all chemical cleaning agents from the stained baking dish.
If it is burnt, soak it overnight in soapy water and use a non scratch scourer. Best wishes.
Here's a post that might help - https://www.ehow.com/how_6065285_restore-corningware.html
Charlotte, if the finish is really bad there may not be much you can do...but the charm on older pieces like yours is that they look used and loved. As long as the pieces are clean, enjoy the memories you have of the dishes prepared in these pieces. Most of us have pieces like this in our kitchens...still using them!
Clean it with comet and a scrubby
Comet will only further scratch the finish, I would suggest something gentler like Bar Keeper's Friend to clean. Once glass is scratched it would need to be polished.... I usually use jewelers rouge.