I recently purchased a bag of Eriksen Keystone filter rocks. These are small, pink, pebble sized grains. I'm told Erik Nording always uses them. You put 3 or 4 in the bottom of the bowl before adding tobacco. They absorb moisture, goop,etc., especially useful if you're a "wet" smoker. Sort of like the Denicotea crystals. I've tried them, and they do result in a drier smoke, and have no adverse effect on flavor. I smoke mostly English type blends. I'd like to know if anyone else has any experience with these. Now here's the thing, I seldom have to run a pipe cleaner through the stem when I'm using them. However, when I do, instead of coming out brown, my pipe cleaners come out black, as if a carbon-like dust were on them. And again, when I clean a pipe in which I've used this product, the cleaners come out pure black, and lots of this black material, and not a trace of brown. It looks like pure carbon, but I wonder what it really is. Anyone on the Forum have any experience with this?