"My wife wants to fire ceramic beads and other small goods so I'm pondering the practicality of building a propane-fired box that also melts aluminum, and perhaps with more effort, heat treats steel or ultimately melts cast iron. Are the functions ... the mechanical arrangements ... different enough that there's no point in attempting to combine all in one? What combinations are workable? The nominal configuration would be a 6"x6"x12" I.D. firebrick box inside a steel box large enough to also contain the burner. Any comments on which applications are really best suited by a nice clean thermostat-controlled electric heating element, and which the propane is better for? thanks in advance ... Bob"

I'm inclined to advise a box-type electric kiln with a sideways opening door for the ceramic beads and heat threating the steel; these are processes that probably could best be accomplished with removable shelves or racks. It's much more accessible that way. The only advantage I can think of for using gas for such a small kiln is the option of controlling the atmosphere for oxidation/reduction of glazes like coppery reds. It depends on how involved the ceramic processes will be. Flames take more understanding, and can provide exciting side effects - like explosions - if the plumbing and burners are not well thought out. I wouldn't use a propane kiln in a house I planned to sleep in. An electric kiln, while still a serious source of intense heat, won't accidentally cause an explosive gas to fill up the basement, and then ignite it.

A cylindrical melting furnace is the standard arrangement for the aluminum (or bronze, I don't know about cast iron, except that it needs to be much hotter). It should have enough space (It's a proportional thing, depending on the overall size and gas volume) around the crucible to allow the gas/air to burn VERY rapidly. A constricted space will choke it out. The flame should enter the base at an angle that sends the flame in a spiral around the crucible, which is raised up off the bottom a couple of inches, and up out the hole in the top lid. This heats the crucible evenly and efficiently, (and causes a satisfyingly loud roar to impress the neighbors). The gas is usually mixed with air by a squirrel-cage blower and directed with a simple steel pipe into the refractory cylinder. It will require a high pressure regulator. Generally you'll want this thing in a shed, away from the home. I made one out of "ramable refractory" material 3" thick, lining the inside of a small steel barrel. Alternately there is a mat-like material available at good pottery suppliers that looks like white fiberglass, but it's a far better insulator at very high temperatures, light weight, and easy to build with. Ask the potters and glass blowers for advise too.

Hope this is useful - good luck.

[and]

"Alan, what is the refractory mat you mention? I have the five gallon can. I was going to get some "fireclay." Is a mat something that may be easier to use than mixing and setting fireclay?"

Refractory Matting is a lot like fiberglass insulation except denser and it's ceramic. I've seen it in pottery supply and glass blowing supply companys. Yes I think it is probably easier than using fire clay, and it's very light weight too. On the otherhand, it is less durable. I made mine to last with "Ramable refractory material" - it's very stiff but viscous stuff that you hammer into shape. Once fired it's just like a firebrick, in whatever shape you made. Strong and heavy. If quality and permanence is your goal this, or moldable refractory cement, is the best I know of. The main disadvantage of the stronger materials is that they take longer to heat up, so you use more fuel.