Don't be fooled by the low-tech appearance, this guy is top notch, he's been doing a ton of research and has quite a bit of experience. You don't set this up the first time out of the gate like this and if you plan on doing any aluminum casting yourself this would be a great starting point.
I also like how he evaluates what he's done, notices what could be improved and makes notes to do those things better next time. That's how you get to where he's gotten in the first place. There are other aluminum melting tutorials out there that make me cringe.
If anybody is wondering why concrete can explode when heated rapidly, concrete will always contain a percentage of water and when you heat that up faster than the steam can escape from the material it will cause a steam explosion.
One question—I thought aluminum was really reactive with oxygen, and normally ever piece of it we see is coated with a thin film of the oxide. Does this present any special issues when heating it up to melt it?
> Twenty minutes later I have melted enough sprues and ingots that the
> crucible is almost completely full. I take the lid off, skim the dross — the
> bits of aluminum oxide and impurities that float — off the top and put it
> in the ingot tray to cool; this will be trash. (Trying to recover aluminum
> from aluminum oxide is not really worth it when aluminum is so plentiful.)
Whether oxidation or reduction is taking place during the melting process is determined by the amount of oxygen arriving via the air blast; too much oxygen and you get a hot oxidizing atmosphere, which oxidizes both my iron crucible and the top of the melt. Too little oxygen and you can actually get a reducing atmosphere, the furnace runs a bit colder, less heat escapes through the flue. So it's a tricky balance to strike and I'm still fine-tuning it.
I add potassium chloride and sodium carbonate to flux the melt and remove dissolved hydrogen; the KCl helps keep more aluminum oxide from forming apparently, though some home foundry sites report that they don't see a difference if they skip that step. Both chemicals are cheap, so I'm not too concerned.
The chemical composition of the oxide  is the same as the lenses on iPhone cameras, the so-called 'sapphire.'
It touches on two stories of personal interest to me. First, my maternal grandfather spent a fair amount of his time in a silver mine in the blacksmith shop. This was a small enough mine that mining was done with picks, shovels and the like. They would wear out, and need to go to the blacksmith shop to be refurbished. We had an old open coal forge that had been used by the previous owner sitting unused in one of our sheds. Grandpa came by one day to fix up one of his pickaxes. The forge had a blower powered by a hand crank. He first scooped the coal out from the hole in the middle of the bottom of the body of the forge. Then took a coffee can, placed it over the hole, and packed coal around the can, and sprayed water on it. He had me turn the crank as he lit the coal, gently at first, then stronger.
Once the heat was up, he began heating the tip of the axe. As he heated, he told stories of how you heat, then cool the tool. Too much heat could burn the tool. And when to take it out to shape the tool on the anvil. And how there was different types of quenching--water, oil. Depending on what the tool was to be used for.
The other story is that my brother (now retired) was a professional welder and instrument maker. He made instruments for telescopes. As a gift, he once gave me a pair of dice made of aluminum. Not particularly fancy, but he noted that the trick with aluminum is that it will suddenly melt on you without turning red.
Metal light emission depends almost entirely on blackbody radiation  which depends only on temperature. Aluminum melts at lower temperatures than iron and that's why iron glows before it melts and aluminum doesn't.
Blackbody radiation is also the principal source of sunlight (and all starlight). It was one of the first physical phenomena that required the quantum theory of energy to explain.
"The project that I am gradually preparing for is to build the Gingery Lathe. The late Dave Gingery wrote a seven-part series of books in which he describes how to build a foundry, lathe, shaper, drill press and other metalworking tools from scrap at a tiny fraction of the cost of buying each. For me it’s not so much the cost savings (or the post-apocalypse skills!) as it is the opportunity to learn for myself how tools work at a fundamental level."
From the comments.
His videos: https://www.youtube.com/user/mintwart
There's tons of material in there on machining and especially metal casting at home.
Why aluminium? Low temp, high availability?
That said, I do have some friends who are experts at working iron, so if I do decide to take it up, I'll have a lot of good advisors.