I ran into this guy. He is doing lost pla casting, and what is interesting is not that he kept failing but apparently there is a special plaster of paris, used for metal casting.
It contains talc and portland cement, plus he added some graphite…and I think dishsoap 
Who was looking for aluminum melting with wood or charcoal?
Wood is used for a casting aluminum is done in this video. Apparently it is all about airflow. It does not look like it gets that hot, but good enough for ingots.
He does a second video, using charcoal using two different charcoal furnaces, one is a charcoal grill fire starter, and the other he cast and forced air with the hairdrier.
Last, this is a good video if you doing backyard work as to things to look out for. there is quite a bit of information in a very short period of time. I think this is a pro-hobby for him coupled with Art. He might actually be a good channel to see other stuff as he also is one of the few people that direct you to OTHER people that are outside his scope of knowledge.
Yes i melt with with wood. With forced air you can get plenty of heat. Ican melt about 10 pounds at a time. You keep pretty busy. feeding in wood chunks tho.
is your furnace just holes in a bucket like that guy had? or do you do something else? and what are you using for a crucible?
I use an old 20lb propane tank with a single pipe in the side. An induction bllower from a furnace provides the air. It has tobe choked down quite a bit., for the crucible, i am currently using the end of what i think is a divers air tank. Its 6" diameter, by about 10 " tall with trunions welded on for lifting.
Last time it took about 1 hour to melt a full pot.
I like this guys design. If i do it again, i will do something like this.
In my current unit, the fire burns most intensly on the inlet side, letting the crucible tip.
His design distributes the air evenly.
It actually provide something for the crucible to sit on besides the wood.
It allows room for a considerable amount of wood to be loaded ahead of time.
I’ve been thinking about how I might make a wood fired melting furnace based on Peter van den Berg’s Batch Box Rocket Mass Heaters. Has anyone seen something like this?
Rindert
Rindert,
My guess is you will still need forced air blowing on the coals to get enough heat. The melting furnace Andy likes above has a large volume of forced air and the whole thing is highly insulated. Your design sketch is promising. Depends on how much draft you can get going! 
I think this would work if, the riser is sized correctly (for the strongest draft), and the crucible is raised up off the bottom.
They used to use charcoal to melt iron. You could easily make a cupola style furnace that burned charcoal to melt aluminum. However, aluminum likes to dissolve hydrogen gas, leading to porosity in the castings. Good foundry practice is to melt and pour as fast as possible, too many things to go bad with slow heating to a melt.
I still have my old melting furnace sitting outside for free, just come and pick it up.
Kent
I think with the batch box, the high temperature combustion is in the heat riser. Secondary air is added going into the riser, so you would probably want your crucible past that point. The dimensions for the batch box are actually very similar to a TLUD, flow-wise, but horizontal, and without the symmetry. You may want a tall riser, and tall stack, since draft is a big deal when you’re after high temperatures.
Well, that’s true. But what makes it do that? I think it’s that rectangular opening from the fire box. I think that if I make a larger, less restrictive, opening at the base of the heat riser, and keep the same size rectangular opening from the fire box it should heat the crucible pretty fast.
Rindert
If you want to try something unusual, (and who of US doesnt), this guy melts aluminum burning leaves.
Sounds like you’ve got it worked out!
edit: You might offset the box with the crucible in it, so the gases and flame swirl around the crucible before they head out to the riser/stack.
