Ceramic is a very hard material, harder than most metals! Because of this, in normal wear it can often become "stained" with residue from other materials. If the ring has a brushed finish, which many ceramic rings do, then the ring acts like a file, and when it rubs up against anything metal, it can transfer some of the metal to its own surface, creating a mark. This can happen during any activity when you are handling metal items, such as while washing eating utensils or using tools. Some metals will more easily transfer to the ceramic than others.
These marks can easily be removed with an abrasive polish, such as Brasso, or glass cooktop cleaner--the cleaner will have a pasty, whitish appearance caused by the very fine abrasive material that it contains. Even most toothpastes will work, though toothpaste is usually not as effective as a dedicated cleaner. Just wet a small area of a paper towel with the polish and rub it on the ring, back and forth in the direction of the brushed finish of the ring. If the ring has a smooth finish, then use a circular motion. It may take several minutes of firm rubbing to remove the mark--you can confirm that you are making progress by rinsing off the ring to check to see that the mark is being reduced in size. If the ring contains gold or silver accents, be sure to not
allow the polish to contact these areas so that you will not remove or damage them.
If you still cannot remove the mark using the above method, you can always take your ring to your local jeweler, who will be able to remove the mark by using a chemical cleaning process.
William C. (Bill) Long