Bonfire

In Kings we read of burning human bones on an altar to pollute it. That's a kind of cremation, obviously--bones shouldn't burn. Right?

At a Geology Museum show the director spoke of burning bones to make smoke. He didn't explain how, but evidently there was something I was missing. He said that the word bonfire came from "bone-fire", and the dictionary says that appears to be correct.

How?

Experiments in Bone Burning: they tried to ignite bones with dry grass on windy Wisconsin days. Not much luck. You have to get the bone hot enough to melt the fat--that's what burns. They tried burning boiled bone too--it was too windy, and I suspect it wouldn't work at all. If you boil them to get the nutritious fat out, what's left to burn?

Instructables offers to teach us how to burn bones, though that's mostly about turning bones into fertilizer. If you prefer something a little drier, try The Use of Animal Bone as Fuel in the Third Millennium BC Walled Enclosure of Castanheiro do Vento: "The various experimental studies that have been published have shown that the use of isolated bones to ignite a fire is completely ineffective. But according to the observations of Théry-Parisot (2002), fires that contain a mixture of bone fragments and wood fuel are longer lasting than those with only wood." You have to love the word choices: "One of the salient features of the use of osteological elements in combustion is the lack of coal production as it happens with fuel wood. It seems that the exclusive reliance on combustion bones cannot be used in the context of long-term fire or for cooking." Hmm. Fat rendered from bones doesn't make long-lasting coals. Who would have guessed?

So the museum director was mostly wrong--if all you have is bones you're not going to get a fire started. But... you learn something new every day.