The charcoal blocks we use are very dense, and they do burn away, but
not aggressively. Because they burn, they are creating heat, not
absorbing it - I assume that is why metal heats up quickly on them.
Most charcoal (like barbecue charcoal) is low density, lots of air
pockets, and burns fast, so is best avoided - suppliers might be
cutting corners by using low grade charcoal.I’m not talking about
reformed charcoal, either - I’ve been told that the really heavy ones
contain cement. They aren’t very pleasant to use, IMO.