That's a flux he puts on. It reduces and eliminates the scale formation when welding, allowing for a clean, solid weld.
He first split the (presumably) mild steel head, and forge welded a high carbon wedge in with it, to give it durability. A flux is usually something like sand, borax or the like. My question is how does he have ANY arm hair if he always tests his tools like that? :blink:
Silly me! I did not think to welcome you! Hello and welcome to IFI! If you put your location on your profile, you may find that there are a few smiths in the area who would be more than happy to show you around, if you ask politely. The search function is invaluable on IFI, so be sure to make use of it! Anyways, welcome aboard, you seem to be off to a good start by taking a class! Thanks for posting the video!