[jonogt]

This might be a bit of a stretch in topic, but I thought it'd be worth a shot to try.

If you don't need to get the big picture farther down the page: 
Are pottery clays and glazes chemically stable enough after being correctly fired  to be frequently heated to ~500F temperatures for as much as several hours with humans inhaling past them?

What I'm actually trying to do:
I do quite a bit of woodworking and general DIY projects, and a friend and I are interested in designing and building a hookah ( http://tinyurl.com/3aa5d2 if you aren't familiar with the device) from a variety of materials, essentially from scratch.  Most of the pipe will be comprised of hardwoods, stained glass, and ornately formed brass. 

Traditionally, the procedure is you load the bowl (the upper-most part of the picture) with flavored tobacco, put a coarse grate over it, wrap aluminum foil over the grate and poke holes through it, and set hot coals on top of it all, which supply heat to vaporize the essential oils and whathaveyou without burning the plant material.  It's a social activity which we find enjoyable, but I do not like the idea of intentionally inhaling fumes from coals.  We want to use a halogen bulb on a dimmer in replacement of the coals, and a glass bowl in replacement of ceramic or metal.

The ceramic concern in this thread is the material for this setup.  A manufactured glass part that suits me perfectly is available for the bowl, but I need a housing for the bulb which I'll have to make myself.  Essentially, I want to sculpt a bell-shaped housing that the bulb will mount in, and the whole thing will be suspended above the bowl.  This will channel clean reliable heat to the bowl, in addition to keeping those nearby from going blind staring at a finger-digit-sized 100w lightbulb.

Is there a specific clay, glaze, and/or firing procedure that I should be looking into for this type of thing?  Sculptors from Holland have made handheld pipes from it and crafters of traditional hookahs have used it in components for centuries, but I can't imagine it's as simple as clay is clay.  I'd like something here that I know would be safe and chemically stable at atleast 500F for periods of several hours at a time.

I've done countless google searches for pottery forums and the like, and none of them are actively used or seem to have any archived info on uses like this.  Can anyone offer some advice, or even a little direction on this? 

Thanks
-Jon

[Arkcon]

Most glazes are vitreous substances, basically glass, so they should be stable.  If they out gas, well, I can't be sure.  Find out what hookah's are made from, and concentrate your search for temperature stability on those specific glazes.  Or just continue to use an unpainted metal bowl, and mount a bowl of similar metal as a light-shade/heat concentrator.

Pretty weird to me 'tho -- you don't want the fumes from coal, which is likely charcoal, pure carbon burning in an open cup, probably completely to CO₂, but you'll take everything else destructively distilled out of moist plant material.