Hey John great to here you back! I don't remember completely, but I think he did not apply any flux. I remember thinking, gee, this looks a lot easier and faster than what I always end up doing (and my results also were a lot more iffy). And the heavier the mass of the parts, the worse it is, for me, normally. Takes a lot of heating to get something big red hot with a torch. He was using coal, by the way, and buried the parts in it to start with while applying draft.
I've seen a lot of impromptu forges online made out of just about anything (brake drums, baking pans, bricks,) , and even remember from Weyger's blacksmithing books a vertical forge made of a gallon paint can, with some stovepipe chimney for draft, hung from a tree. Seems to me just about any receptacle, supplied with any form of draft, given some charcoal will probably do the trick. True, purpose built forges with insulation, a blower, propane burner, etc. might be classier and more efficient, but no reason not to try to use what's available, rather than go without --- if our interest is up..... that's my tendency
