The process by which wood (or sawdust, coconut shells, bone meal, even dried buffalo dung!) is converted into charcoal is called carbonization. Essentially, wood is primarily hydrogen, oxygen, and carbon. Carbonization removes the hydrogen and oxygen (and trace impurities), leaving only the purified carbon. If burned in an open flame, the carbon would go up with the other elements, so charcoal is produced in environments of restricted oxygen. Typically, the wood (or other material) is loaded into a container, or in more traditional methods, simply buried under carefully arranged logs and soil, and a fire started within. Once the fire is going strongly, the main chimney is sealed up, leaving only selected vent holes which regulate the flow of oxygen into the burn.
The primary physics behind a hookah bowl involves drawing very hot air from around the coals through the shisha, vaporizing the sugars and oils into smoke, which is what makes the Hookah Flip Bowl so particularly efficient - hot air rises! Burned bowls will result from excessive heat - either too much charcoal, or charcoal which has sat so long in one spot on the shisha that it begins to cook and burn the shisha from the radiant heat. Minimizing contact with the bowl, as seen in the design of the new Fantasia Hookah Coals, also maximizes the flow of hot air while minimizing the proximity of the heat-emitting coal. Happy smokin!
, the smoke giving spirit of the hookah. A vessel containing the power once stolen from the gods and bestowed on man. Formerly, a tree. Man has made charcoal for eons, ever since it was discovered, somehow, that it burns hotter and more cleanly that simple dry wood. On average, a typical dry wood will burn with an energy value in the neighborhood of 14 or 18 MJ/kg. Charcoal, on the other hand, has an energy value of 29 MJ/kg. Additionally, wood expends much of its heat in radiant energy, whereas charcoal retains more of it (hence, burning longer). Another difference between charcoal and wood is the purity; the carbonization process removes many resins and prevents incomplete combustion, which creates numerous new chemicals that form when wood is burned. That's why one can say that charcoal burns more cleanly, and is why burning charcoal doesn't emit smoke (though, as with any source of ignition, CO2 will still be produced).