We Do Not Recommend Making a Sword With Thermite, But Hey
Thermite, a mixture of powdered iron oxides and aluminum, can be burned to produce temperatures it would be hard to argue are truly safe outside of a meticulously controlled environment (over 4,000 degrees Fahrenheit / 2,200 degrees Celsius). It's used for a variety of purposes, from metal cutting and welding to military incendiaries.
It can also be used, apparently, to very quickly whip yourself up a sword (albeit not necessarily a very good one).
As he also admitted, it was heavy, did not appear to have an ideal physical composition and its cutting edge was pitted through, so this is probably not something you would want to use on a battlefield.
Please don't try this at home, but if you do, don't wear shorts.
[ YouTube ]