I went ahead and used the ol' magic eraser on what I would consider to be four of the Empress chips with the worst markings. Here's the before and after.
Before:
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And after:
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As you can see, the magic eraser definitely cleans up some of the markings, but the very worst still remain. Maybe with a little extra time and elbow grease the marks would get completely eradicated? Regardless, the magic eraser DEFINITELY helps and is effective to a significant degree.