Pressure Flaking
Pressure flaking involved pressing a section of bone or antler against the platform edge and increasing the pressure until the crack initiated and a flake was removed. The stoneworker could be very precise in the location where they set the tool and the direction of applied force.
The pressure flaking technique involved static loading of force onto the platform, in contrast to the dynamic loading seen in direct and indirect percussion. Static loading resulted in a more stable crack path. The pressure technique was usually applied by using the muscles and weight of the body to build up sufficient force for the flake to initiate. It was possible to achieve very precise and aesthetically-pleasing effects using pressure flaking.
In making bifacial tools, Native Americans held the core (a flake or biface) in the palm of their non-dominant hand and applied pressure with the flaker held in their dominant hand. In Australia, flintknappers held the biface in their fingers with one edge supported on an anvil. Pressure blade-making was achieved using a variety of complex techniques. The pressure-flaking technique was used on fine-grained stones.
A prominent ridge could be set up on the centre of the face of a pressure-flaked tool by using a technique that maximised the outward stresses that drive the flake path—the flake would feather-terminate near the middle of the face. The central ridge was enhanced when matched by flakes removed from the opposite edge. A slotted block was likely used to achieve this, where the flake detached in the free space provided by the slot. Alternatively, a core holding technique could be used where the flake detached uninhibited, as practiced by flintknappers in the Kimberley region of Western Australia. For a different effect, the face could be constricted—such as held against the palm of the hand—which increased the stiffness of the detaching flake, encouraging it to roll over the centreline before terminating. This style of pressure flaking produced tools without a defined central ridge. Pressure-flaking tools were usually relatively short shafts with rod-shaped tips that were held in the hand. The pressure flakers were often equipped with handles to make them easier to hold. Ishi, a Yahi flintknapper from California, tied his pressure flaker onto a long handle now referred to as an ‘Ishi stick’. This tool allowed the build-up in more force to the tool’s tip than could be achieved by a short tool. Long single-piece antler pressure flakers have been recovered from archaeological sites in Northern Europe. Pressure-flaking tools were usually made from antler or bone, but certain varieties of very hard wood may have also been used. For effective pressure flaking, the edge of the core must bite into the flaking tool, and stone was generally unsuitable for this. Soft metals such as pure copper, copper alloys, or soft iron can be used as pressure flakers. The majority of modern flintknappers use copper pressure flakers because it can be worked into a stronger narrow tip than antler or bone and is more resistant to attrition. Copper alloy ‘awls’ may have been used for pressure flaking in Chalcolithic Europe and South Asia, and some researchers have suggested similar copper awls may have been used for pressure flaking by Native Americans. Sections of iron fencing wire were used as pressure flakers in the recent past to make dart points in the Kimberley region of Western Australia. Modern ‘lapidary knappers’ do all of their work by pressure flaking with metal-tipped tools. The earlier stages of reduction, to set up the blank for pressure flaking, is achieved by cutting blanks from the stone using rock saws, thus avoiding percussion flaking altogether. The sawn blanks are sometimes ground into a smooth biconvex cross-section, which is ideal for detaching pressure flakes. This allows for very precise, aesthetically-pleasing sets of flake scars to be produced on the finished point or knife.
Collateral Pressure Flaking
Selective collateral pressure flakes were removed in a non-patterned way from various places along the edge to shape and contour the biface and flake. Serial collateral pressure flakes were removed in a sequence, one after another, down the tool’s margin. This could create an attractive pattern of flake scars on the tool’s surface, which may have been one motivation for using it.
Collateral pressure flaking was commonly used in later prehistory to shape and resharpen unifacial and bifacial projectile points and knives. It was sometimes used to resharpen the dull or clogged edges of retouched flakes. Collateral pressure flaking was reinvented in many times and places around the world.
Transverse-Parallel Pressure Flaking
The stoneworker applied oblique force because the expanding flake would tear away part of the tool’s platform edge. This created an arris to guide the next flake, which also would tear away the adjacent part of the platform edge. When applied in series, this ‘tearing’ effect could create an extremely sharp edge—indeed, this is the sharpest edge possible using a retouching technique. The obliquely-oriented flake scars were also aesthetically pleasing, which may have also been a motivation for using the technique.
Often the tool was held in the hand for this, and because the constriction by the palm stiffened the flake, it was possible to push the flakes completely across the tool’s surface. Platform attrition was minimal and thus the transverse-parallel technique could significantly thin a tool relative to its width.
Transverse-parallel pressure flaking was commonly used in later prehistory to shape and resharpen unifacial and bifacial projectile points and knives. It was sometimes used to resharpen the dull or clogged edges of retouched flakes. The technique was reinvented in many times and places around the world.
Pressure Blade Making
Skilled flintknappers were able to quickly produce many sharp-edged blades with parallel edges and uniform cross sections. The blades were ideal for using in composite tools.
Extensive industries arose in the Neolithic and Chalcolithic periods to supply millions of pressure blades to market economies in Europe, Western Asia, South Asia, and Mesoamerica. In parts of Europe and Western Asia, levers were used to create parallel-sided blades measuring more than 25 cm long. A pressure technique was used by Aztecs in Mexico into the historic period to make obsidian blades for weapons and tools. Smaller pressure microblades were elements of toolkits in Pleistocene and Early Holocene Eurasia and the Arctic of North America.
Cores were initially manufactured by direct percussion to set up the platform and initial ridges on the core face, prior to the switch to pressure to make the blades. A discarded pressure blade core is often bullet-shaped with a fluted appearance resulting from blade removal. In pressure blade-making the core must be immobilised in a vise to ensure balanced crack propagation to the bottom of the core and to prevent overstruck terminations.
The vices have yet to be discovered in the archaeological record, but experimental archaeologists have worked extensively to come up with plausible simple vices made from natural materials such as bone or wood. Organic pressure flakers—probably bone or antler—were used to detach these blades, and researchers in South Asia have suggested that copper alloy awl-like tools were used to make pressure blades during the Chalcolithic period.
