My problem seems to be like none of the others I read. My corelle coffee mugs are covered on the outside with gray marks. Strangely, the gray marks are absent for about an inch on each side of the handle (i.e., that 2" space is completely white). The gap in the gray marks corresponds exactly with the gap in the pattern around the top of the mug. The gap in the gray marks is sharply defined, i.e., the white area starts and stops at very straight vertical lines. All 8 mugs have the same problem.
I tried all the suggestions for cleaning and they did not work. I also tried Magic Eraser.
© RDA Enthusiast Brands, LLC 2016