In the 11-minute clip, uploaded by YouTube user Kiwami Japan, the prolific knifemaker documents himself flattening a standard roll of aluminum foil using a hammer, then heating the resulting thick and narrow slab over a gas stove to make it even easier to get flat. Once he's compacted it pretty well, he traces the outline of an actual chef's knife onto it with a Sharpie, and cuts the edges using a hacksaw. Next, he heats it up again, flattens it some more, and takes some sandpaper to sharpen the edges, and then uses a series of whetstones to further sharpen the blade. Eventually, he cuts a handle out of wood, fastens it to the blade with a pair of screws, and buffs the whole thing with some more sandpaper to give it the sort of finish you'd expect to see on a pricey piece of cutlery at Williams-Sonoma.
All in all, it's an impressive display of skill, although it clearly involved quite a bit of time and patience. It's also unclear just how long a knife made from aluminum foil will hold up against normal wear and tear. Then again, who cares, you can just whip up another one whenever it goes dull.