Over time, silverware and stainless-steel flatware can create gray marks on your dishes. The marks are caused by scraping the utensils across the surface of plates, bowls and cups. They can become especially dark on stoneware and pottery. If you try to clean them off with plain dish soap, they can seem impossible to remove. However, with the right cleansers and a little bit of elbow grease, you can remove the discoloration and make your dishes look as good as new.