I've heard this too. I stopped using salt on my clear pieces (bongs). Hot isopropyl alcohol warmed in the microwave is the best alternative. Plus hot iso is much better on tree percolated pieces than salt, as those arms are not made to withstand the extra weight and could eventually break from it after many (or not so many) cleanings. So yes, hot iso on clear pieces, salt is OK if you're cleaning a colored piece. EDIT: By the way, the thing about the micro-abrasions came from a glassblower who will not clean his pieces with salt anymore. I didn't get to see the tube he says has a lot of the micro-abrasions, but this guy has no reason to lie to me.