Bipolar Flaking: Variability or Chaos
BIPOLAR UNIFACES BU: Introductory BU: Quartzites BU: Proximal Fractures About Author

BIPOLAR REDUCTION: Variability or Chaos

Christopher Hardaker, Tucson, AZ


This is a site dedicated to those few who have chosen to spend a good portion of their lives studying stone tools, their production, function and refuse. The presentation offers the viewer a glimpse of experiments in bipolar flaking, its forms and variability. It will be a photo-heavy site, so the faster your machine the better.

Please excuse the condition of the website, a first attempt. It is a cyber-version of a draft article with illustrations pasted together on pages. It is a site of few frills, and to navigate you will probably have to use your BACK button quite a bit.

The material that follows represents an ongoing concern regarding causes of lithic variability and their possible misidentification. Experiments with bipolar reduction techniques have generated a range of forms and fractures that could be misinterpreted. The presentation is best considered a slide show overview of the formal complexities that attend this kind of reduction.


It is assumed that the visitor to this site is already familiar with the basics and the refinements of direct percussion and pressure flaking strategies. Instead, the focus is bipolar flaking, and to a lesser extent block-on-block flaking. For most, bipolar reduction has come to represent an expedient last resort way to get a sharp flake that also generates a lot of shatter. To some extent this is true. From an evolutionary and strategic perspective, it is the same process that takes place when you crack a nut between two rocks, or lay a large limb bone on a rock and hit it with another rock -- this generates a spiral fracture which makes available both marrow and sharp bone edges. Researchers of early assemblages in Africa and Asia often mention bipolar as a source of some of the lithics turning up; these assemblages often include unifaces.

A primary reason for the focus bears on the epistemological nightmare offered up by experiments in bipolar flaking. Residues of this powerful method are often characterized in terms that emphasize a high degree of chaos, most notably the term "shatter" comes up a lot. Shatter is generally defined as chunks, slivers and pieces that do not fall under the archetypal fan-shaped or blade-like flake (which also occur). These initial pages will be devoted to dispelling some of the myths and rumors of bipolar flaking. One of the myths has to do with bipolar flakes possessing bulb formations at their proximal and distal ends. Theoretically and physically this is a common phenomena; but more often than not, the flake that possesses this feature will break at the point where the two forces meet. To an analyst, the flakes could represent two proximal flakes generated by two distinct percussion strikes. Another myth is that bipolar residues can be typified -- presently I don't think that is true because much of what you will see here overlaps with common flake types on the one hand to extremely odd pieces that would normally be associated with Nature's handiwork.

During the past twenty years I have had the pleasure of meeting some of the best flintknappers and lithic specialists in the States. However, bipolar reduction experimentation was rarely examined seriously -- with a few notable exceptions such as J. Flenniken's dissertation on bipolar reduction of quartz and N. Toth's work with early African assemblages. Many flintknappers, both archaeologists and avocationalists, have told me they have no interest in experimenting with bipolar because it does not require skill. This could be true; more to the point, bipolar is not a "craft" in the way that bifacial thinning is so considered. For many, the ramifications of bipolar reduction are a dead-end. This is an opinion that the following pages will hopefully reverse.

The significance of bipolar flaking has to do with Variability, not skill or craftsmanship. Once you reach a point in bipolar reduction competency, you cannot get better at it and you cannot predict the exact (or even near-exact) morphologies of the residues. Some of our ancestors were not driven by this need. Ethnographic accounts from New Guinea support this claim. On the other hand, there are "patterns" that seem to coincide with bipolar reduction. Some of these patterns are included here, but it is only a beginning and probably just scratches the surface. Relative to the more craft oriented reduction techniques like hard and soft hammer reduction and pressure flaking, the seeming technological chaos that accompanies bipolar reduction makes it a good candidate for representing the more expedient aspects of our natures, such as using a coin for a screwdriver.

Direct percussion, pressure flaking and the like can all be categorized under the single flake type that we learned in Archaeology 101: platform, bulb, bulb scar, concentric rings/ripples, and occasional radii that extend out from the bulb running perpendicular to the rings. Regardless of whether the flake is knocked off a 300-lb boulder or it is a pressured flute flake from a Clovis point, the flake will share these ventral qualities because the techniques depend on the same basic kind of conchoidal physics. Behaviourally, the ideal would be: one strike, one flake. Theoretically, each flake represents one successful strike. Mistakes happen, so this is not always the case. But, in the mind of the knapper doing the striking, I think it is a valid template; that is, every time he strikes he expects a successful flake release.

To be sure there are many varieties and many techniques included under the umbrella of the direct percussion model; back about twenty years ago, Flenniken's students talked about his list of 200-300 known techniques. I have not seen that list, though I would hazard a guess that all but a few could be housed under the direct percussion model: hard and soft percussion, indirect (punch) percussion, pressure flaking (including chest punch). Regardless of the number of techniques falling within this category, they still produce flakes sharing the basic force signatures: There's the platform, the bulb, the rings, etc. Another fundamental characteristic of these reduction techniques is that they can be controlled -- you can learn to control them. From a metaphorical-evolutionary perspective, you participate in a couple million years of technological learning every time you take a rock or large flake and first turn it into an ovate biface (aka handaxe, coup de poing, Stage One) and end up with a Solutrean laurel leaf or Clovis point (aka Stage Four or Five, depending on who you talk to). Fundamentally, the biface is wrapped up in the phenomena that occurs during alternate flaking of a single edge: when you remove a flake from an edge, you automatically produce a rough platform structure for a potential flake removal on the opposite side of the edge. You learn to look ahead. You learn to value your platforms.

At the 1980 Little Lake Knap-In, sponsored by the folks who brought you Flintknapper's Exchange, a variety of direct, indirect and pressure techniques were on display during the Clovis replication section of the planned activities. As the bifaces became thinner, platform preparation took longer. You get to this stage and you start to plan your strategy: what first, next, next -- before you do much hitting at all. This is the nature of the craft as you get better at it. Like sculpture, the art is in the removal of material, not its addition (e.g. textiles, ceramics, architecture): a difference between controlled subtraction and construction.


It would be impossible for me, a bipolar experimenter, to predict residual morphologies of the bipolar process. The one strike-one flake template does not exist. My only true expectation is the production of Edges, edges of all kinds, sharp and broad and everything in between. Bipolar flaking, as a method, may include only two actual techniques, and I am sure even this may be disputed when the viewer examines the bipolar unifaces. Because of the seemingly chaotic fractures and residues of bipolar flaking, the Internet provides a perfect medium for data sharing. A couple examples illustrated in a journal article cannot give the reader an appreciation of what we as a community may be up against as we struggle to identify not only bipolar residues from those of direct percussion, but as important, to discern bipolar residues (human intent) from Natural fractures. Three artifacts are presented for the reader to consider in light of experimental data.

Much has been said but little has been written concerning concrete ways to tell the difference between human and natural agencies of fracture. Even now there are varied opinions regarding the artifactual nature of the lithic assemblages uncovered during the Diring site excavations in Central Siberia. It still seems to be a problem because there remains a good deal of perceptual overlap, as the viewer will experience in these pages. Another page of the website illustrates several examples of natural fractures found in the field. Many more are needed, and it is hoped that others will also either post or send in their favorite examples.

Every technique that uses the direct percussion model strikes the core at a point on or close to its edge (with certain obvious exceptions such as striking off the end of a pebble or cobble in order to make a platform to work with). Bipolar flaking directly assaults the entire mass of the core. The relative chaos of bipolar flaking is generated from the awesome amount of energy harnessed when a large hammer (maul) hits a much smaller core standing vertically on a large buried (stable) anvil. How much energy? Is it just an initial force being rebounded by the anvil? How simultaneous is the rebound force to the initial force? Are there a range of forces that bounce back and forth within the mass of the core? Are there different waves or resonances that occur? (IF you know of a reference that details this information, please send it in.)

If there are any incipient fracture lines in the core (often characterized with chemical staining), you generally find out in a hurry.

Multiple flakes and chunks can be generated simultaneously from either end of the core as the result of a single hit: what does this do to the adequacy of present methods for assessing flaking angles?

Different materials fracture differently; that is, they express the forces generated from bipolar reduction differently. This adds an extra dimension to its range of variability. Direct percussion flakes struck from quartzites, cryptocrystallines, obsidian and basalt all share a similar suite of signature features (platform, bulb, etc.).

The results of battering on some cores can easily be mistaken for hammerstone usewear in the eyes of the uninitiated. That which is battered in this way takes on the appearance of tools doing the battering.

So while the craftsman may look askance to the chaotic and uncontrollable world of bipolar flaking, it is hoped that archaeologists and other specialists interested in the domain of lithics, but unfamiliar to bipolar variability, will enjoy and benefit from the pages and photos that follow.


A goal of this presentation is that viewers will attempt this radical reduction technique for themselves, which brings up a couple warnings.

1. Different core materials succumb to the forces of bipolar flaking in different ways. Don't try to blast through an obsidian pebble or cobble: much loss of blood awaits and many bandaids needed, possibly surgery. The only place I know where obsidian was broken with bipolar was in the prehistoric Southwest using Apache Tears, which was okay -- these small obsidian pebbles were only a couple centimeters in diameter. Instead, given the expedient nature of the techniques illustrated here, try experimenting with your local or common (non-exotic) materials, preferably packaged in pebble or cobble form. It may provide more reliable comparisons with the prehistoric lithic assemblages in your own archaeological region.

2. Be sure the anvil is stable, preferably buried. It should be big enough not to move or wobble during the hit. The hammer must strike the core dead on. Therefore, it is best to lightly hit the held core a couple times to make certain that resistance is at a maximum. If you come down on the core and the anvil wobbles, well ... some call it Knuckle City.

3. Over-estimate the size of the maul so that you do not have to muscle the blow. Knowing what size to use comes only from hands-on experience. By selecting an overly large hammer, your attention can be devoted to just guiding it to the top of the core, allowing it to drop of its own weight. Remember: What you are trying to do is to set up a complex of forces so that they work themselves out in the core. When you try to muscle the blow, at least early on in practice, it could be very dangerous where not only your knuckles but entire hands may discover the acute realities associated with spiral fractures. By holding onto a large maul and allowing it to drop of its own weight on a held core, your muscles will be ready to pull the implement away from the core quicker if/when the strike wobbles the core.

Any questions or comments:

Chris Hardaker
Tucson, Arizona