Coke Pepsi, pour in and let sit for a few hours. Denture cleaning tablets, add water and let sit or worst case senario; Easy Off Oven cleaner and follow directions. I use spray on oven cleaner to remove acrylic paint from several pairs of jeans and it worked like a charm. I use oven cleaner to clean my glass baking pans but do this outside and wear a mask. It contains lye so it is not good to breath. Good luck.