Smoking - crack / freebase cocaine ash

[klaatu]

My first post here. Hey, you gotta start somewhere!

Ok then. SWIM is old (I mean like 40!) and has never, ever done any drugs. Swim doesn't even smoke cigarettes. But then one day is tempted by a pretty young lady to try crack. Mmmm.... nice. I mean the lady as well as the crack of course )

So, swim has a lot of learning to do and the friendly neighbourhood internet supplies all the answers. Except one. Why do people put the rocks (or in swim's case they are so small he calls them gravel) onto a layer of ash?

I mean I've searched the forums here and found all the references to ash, but no-one actually says +why+ they use ash.

I suspect it's to stop tiny little bits of crack from dropping through the holes / mesh / gauze / whatever. But then what do I know?

People far cleverer than swim say "Use ash", so swim uses ash. But swim doesn't smoke so getting cigarette ash is a drag (no pun intended. Ok, so I'm a liar - it was!)

Swim will be happier if the clever people here can tell him +why+ ash is o important....

TIA