Last weekend I was rendering wheel weights using my burner and my dutch oven, and it was cold out, so it was taking a long time to melt and sustain the melt.
So I took some sheet metal and formed it into a big loop, making a shield around the whole pot. As it was burning on the burner, I also took a big wad of fiberglass insulation and laid it on top of the pot, mostly filling the "baffle" I made to surround the pot.
This lets the heat that rolls off the bottom of the pot surround the sides of the pot. More heat goes into the lead and less out into open space. This drastically improved the melt time, which saves gas.