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Stone tool making 101: the mind of a modern knapper

A recent Science essay suggested that symmetrically shaped hand axes are precursors to symbolic behavior because making one requires holding a mental image of the finished product in your head. Origins asked a modern knapper, Steven Goldstein, an undergraduate anthropology major at Stony Brook University in New York state, to describe his thoughts as he created a stone tool.

A hand ax is a teardrop-shaped stone tool that you make by flaking off pieces of stone from both sides or “faces” of a stone, forming a sharp cutting edge. For more than 2 million years, early humans produced various kinds of these cutting tools.

I’ve had a lifelong interest in archaeology, and to better understand the process of making chipped stone tools, I began teaching myself how to replicate them. I started with Oldowan tools and eventually moved up to Neolithic and New World materials. Here’s what I do, and what I think, while I make an Acheulean hand ax, which early humans created about 1 million years ago.

A large percentage of functional Paleolithic hand axes were probably made in advance of jobs such as meat processing and woodworking. To make my tool, I anticipate a need, consciously decide to prepare for it, and imagine the shape and size of the tool I will need. Early humans used a variety of stones, including (but not limited to) quartzites, volcanic rocks like obsidian, flint, chert, and shale. With little high-quality material locally available around Stony Brook, I’m restricted to what I can buy or exchange with other knappers from around the country. In this case, that means angular cobbles of a low-grade flint.

I select the flint cobble that is the closest in its natural shape to my desired final product. Having seen hand axes in museums, class lectures, and published reports, I can easily imagine their schematic shapes (though of course I can’t assume my perception is the same as an early hominin’s). I’ve also collected a few hard, fist-sized quartzite pebbles of different sizes to use as “hammerstones.” Sitting over a tarp out behind the Social and Behavioral Sciences building on campus, I get right to work. I pick up the heaviest hammerstone (which will generate the most force) and hit it fairly hard against the side of the cobble. There’s a loud crack: I’ve just successfully removed a large, broad flake. I do it again and again, moving along the edge created by the previous blow and forcefully taking off large flakes from the cobble. Most of the thinning and shaping of the tool occurs in this primary stage, and so it’s important to remove large flakes. This photo shows this early stage:

The cracks continue. Flint-knapping is very loud, and on the African landscape it could have effectively been a dinner bell for predators. As a modern flint knapper, I’m more likely to attract concerned looks from passersby—or another archaeology student who wants to join in.

The ends of the flint cobble are round, and I need a nice sharp point on my hand ax, so I strike the rounded end at an angle and form one side of the hand ax’s pointed end. This also creates a platform from which I can take off additional flakes to form a thin tip with sharp edges. The end of a stone tool needs to be thinner and less massive than the middle, otherwise it’s likely to break under the blows of the hammerstone. With that threat averted for now, I can return to removing large flakes along the perimeter of the tool, making my way back to the base.

Sometimes my blows don’t work quite right, and the flake stops short, leaving a sort of lip or step on the tool’s face. These “mistakes” rarely affect the cutting edge directly, so I can ignore them, although they do create flakes with a reduced cutting edge. If such a mistake does interrupt the edge of the hand ax, I can strike from the opposite side of the same face, creating a long flake that runs underneath the error and removes it. These flaws are common in Paleolithic hand axes, and while they are to a degree relatable to the skill of the knapper, on some types of stone they can be nearly unavoidable.

I keep working until I have the rough pear shape of a hand ax with flakes removed from both sides of the cobble. Little of the original “cortex,” the rough weathered surface of the stone, remains. Many hand axes have cortex still on the base, but I remove it in favor of a flatter profile and more cutting edge.

Throughout this process I’ve been accumulating cuts on a few of my fingers from shattered bits of stone. Flakes from many types of stone are sharp enough to slice to the bone, but fortunately mine are all fairly shallow. With a little soap and water I’ll be fine, but infection could have been a serious concern in prehistory.

I now take the smaller hammerstone and grind it along the perimeter of the hand ax, removing the sharp ends of the edge, dulling and thickening it so that I can take off another series of smaller flakes. The edge would be too thin otherwise, and a blow from the hammerstone would just crush it. As with any part of flint-knapping, this “secondary flaking” reduces the size of the final hand ax, but it also straightens and sharpens the cutting edge and gives it a more exact symmetry. This isn’t a functional necessity, and in many cases, secondary flaking is only from resharpening.

My finished hand ax is not as thin or as well shaped as some I’ve seen, but it still has a certain aesthetic quality and it fits the mental image I had in mind. I also now have a pile of razor-sharp flakes that are extraordinarily effective cutting tools on their own. With very little effort, these flakes can cut right through thick leather or animal hide and separate meat from bone. (Flaked obsidian is actually sharper than surgical steel.) The whole thing took roughly 20 minutes. I’m not too tired, though I would be if I did this for hours, especially if working with large cores and heavier hammerstones. Here it is:

Some archaeologists such as Peter Jones and Sally McBrearty have pointed out that the hand ax’s shape is just a maximized cutting surface with a minimum weight, and we should be careful how much we read into them. You do need some kind of mental template to produce one, but for me, making a stone tool is an entirely technical process, not an artistic one. Making hand axes requires simultaneously considering a lot of factors outside of banging rocks together, including raw materials and fracture mechanics.

The process varies between fun and frustrating, but it’s difficult to not be pleased when you succeed in completing what you set out to make. Everyone loves stone tools, so I sometimes give the finished products as gifts, but most of what I make gets stored in case I need them one day for experimental research.

Jones, P. R. 1994. “Results of experimental work in relation to the stone industries of Olduvai Gorge.” In M. D. Leakey & Roe, D. A. (eds) Olduvai Gorge: Excavations in Beds III, IV, and the Masek Beds, 1968-1971 (pp. 254-298). Cambridge: Cambridge University Press.