Here is a photo showing my natural combo slurry stone along with .... to my surprise .... my vintage blue/green Escher is lighter on top than on the bottom half. The sides had many years of patina that I didn't disturb. The full bottom label is rough but intact so upon taking a closer look I scrubbed the sides with a scotch brite pad and some comet. Lo and behold it is a two tone stone. :y Looking at the photo, the differences in the larger stone on the top, looking down at the side are subtle but there are two distinct colors. The slurry stone is obvious. I would never have known had it not been for Scipio starting this thread. :bow