One of the iconic weapons of the Paleolithic era is the fire-hardened spear, the wooden point of which has been charred by fire to a bad point. Unfortunately, it turns out that our hunter ancestors were wrong about fire hardening. Yes, the charring can make wood slightly harder, but it becomes so much more brittle and weak that there is little overall improvement to the weapon. After experimenting with their own fire-hardened spears, a group of British biomechanics researchers now believe that our ancestors used fire not so much to make a deadlier weapon, but to speed up the process of chopping wood to a point .
The oldest spear ever discovered, the Clacton spear (named for the region of England where it was discovered), dates back to 450,000 years ago. Created by some unidentified ancestors of modern humans, the sharp wooden tip was broken off and buried in the ground. There it was shielded from the elements and kept much longer than normal wood can be. When the Clacton spear was discovered in the early 1900s, archaeologists noticed that the tip was fire-hardened, a technique that some hunter-gatherer groups still use today. It was long believed that heating a pointed spearhead in fire was a way to make it sharper and harder. But a new article published in Biology letters from the Royal Society suggests otherwise.
Two bioscientists at the University of Hull, Roland Ennos And Tak Lok Chan, decided to find out for ourselves if fire really makes spears harder. So they harvested 20 rods from local hazel trees and abused them for weeks in machines for very precise, codified destruction. First, each bar was divided in half. One half dried naturally in the lab for two weeks, and the other half received a simulated fire-hardening treatment using an experimental setup technically known as a “disposable barbecue.”
“The bars were placed on a disposable barbecue with glowing charcoal,” the researchers write. “They were rotated continuously while the internal water was expelled and then heated further. The rods were removed as soon as they turned brown, but before they started to turn black, although two samples started to char and were discarded.”
They then tested each bar for hardness, as well as how it responded to bending and sharp impacts. What they discovered was that the wood being fired was slightly harder, but also significantly weaker. Compared to the unfired control rods, the strength of the fire-treated hazel rods was reduced by 30 percent, and the “breaking work,” or ability to resist breakage along the grain after impact, was reduced by 35 percent.
So it seems that fire hardening probably did not improve the overall effectiveness of spears. Any gain in hardness would have been undermined by brittleness. In fact, this very brittleness is why the Clacton’s spearhead broke off in the first place. The researchers suggest that fire-hardening may have started as a time-saving device. Instead of having to dry and painstakingly cut through a green stick, an ancient human could slowly roast it in the fire and scrape off the ashes to make a sharp point at the tip. In their paper, the researchers conclude that firing dramatically reduces working time. “It has been shown, for example, that the Clacton spearhead could have been produced by shaving the butt with a sharp ‘Clactonian notch’ flint blade, but that this process could be accelerated from 2 hours to 45 minutes by alternately charring the point and removing the char layer with the notch,” they write. “Fire hardening of spears may therefore have arisen as a by-product of their manufacture; the benefits of the process are ambiguous.”
So maybe our spear-throwing ancestors didn’t dip their guns in fire to get even more hardcore. They were just trying to be productive with their time.
Biology letters from the Royal Society2016. DOI: 10.1098/rsbl.2016.0174