Ok, here's the whole glycerin thing again, maybe it's time to shed some light on the whole thing. It goes like this :
Glycerin, although looking like some fat substance is actually an alcohol with the chemical formula CH2OHCHOHCH2OH. For sake of simplicity we write C3H5(OH)3. when heated, it reacts with Oxygen this way :
2C3H5(OH)3 + 7 O2 -> 6CO2 + 8H2O. the co2 molecules just "fly" away, and the water molecules evaporate under the action of the coal heat and that's how you get bigger CLOUDS(good term for something that's basicaly a small cloud, right?
Why do we have to be careful with glycerin? Well this is why some tobaccos need sometimes to be left out for a few hours, because too much glycerin + heat without enough oxygen will give you the dreaded Propenal(or Acrolein), which is basically a toxic substance.
This is why when i first tried my al waha i almost fainted, and after leaving it to air i had no problem. What it all comes down to is add just A BIT of glycerin and you get bigger clouds. Add even the tiniest more and you can kiss the flavour goodbye and also get a great chance of huge migrains. I personally have a small bottle of glycerin just in case i get some tobacco dried up, but other than that there shouldn't be any need. Hopefully we won't see more threads about glycerin