A charcoal block with a groove carved into it always works for me.
The charcoal retains and reflects the heat very well and also reduces
the oxygen, allowing me to use as much oxygen in the flame as I need
to get it hot enough to melt. A pinch of borax powder for flux and a
quick stir with a wet chopstick or graphite rod after melted picks up
the worst of the foreign material that might be in it.
Also, I’m using propane, not acetylene, with the largest tip of a
Smith Little Torch or, for larger amounts of metal, the rosebud
(multi orifice) tip.
James S. Duncan, G.G.
James in SoFL