The stone is slate backed and it is flat and you can't feel the pores. It almost has a shiny metallic look to it. wish I could get better pictures of it. It was sitting in a plastic tub that I keep alot of my other honing stuff in like stone holders and my other coticule and some other stuff. Most of the rest of my stones I keep in boxes. It didn't even dawn on me that my other coticule is a combo and was sitting on the top of this one for awhile and maybe with the BBW on top might have caused it. I thought coticules were non porous though. I was thinking maybe it was like some that will change color in sunlight. Thanks for all the info.