Flake Morphology

Core

A core is any piece of material that has had flakes removed from it. Thus, a core could be used only as a source of sharp flakes, as in this example. At other times, cores themselves might also be made into tools, in which case the resulting tool is called a core tool.

Flake

A flake is any material removed from a core, whether intentional or not. In some cases, the flakes themselves were meant to serve as tools. In other cases, the flake is further modified to make a tool. At other times, the flakes may just be the waste material from shaping, thinning, or resharpening a stone tool. This waste material is called debitage, and is one of the most important collections of lithic material that archaeologists study. By studying the waste flakes and failures, we can actually reconstruct the prehistoric production technology and gain valuable insight into an important component of prehistoric human behavior.

Flake Scar

The flake scar is the concave surface left on a core after a flake has been removed from it. The flake scar will show the reverse image of the bulb of percussion on the flake, and will also exhibit ripples on occasion. The flake scar is equivalent to the hole left in the window pane from our last example.

Cortex

The cortex of a core or flake is the weathered, outer surface of the rock. Archaeologists often examine flakes to determine the amount of cortex on them in order to gauge the stage of manufacture and the degree to which cores were being used to exhaustion.

Striking Platform

The striking platform is the prepared surface on both the flake and the core where the blow that detached the flake was struck. Striking platforms will have different characteristics depending on the technique that was used to remove the flake. For example, on this flake and core, the striking platform has only one surface, and is quite wide, indicating that the flintknapper wanted to detach a large, thick flake. The platform will often have half of a ring fracture right at the exact point where the detaching blow was struck.

Errailure

The errailure is a French term denoting a subsidiary flake scar on the bulb of percussion of a flake. These scars occur as a result of excessive force being applied in the removal of the flake. The bulb of percussion is compressed so much that its elastic response is violent enough to cast secondary flakes off of itself.

Bulb of Percussion

The bulb of percussion is the conic section resulting from the fracturing of the rock. Depending on the amount of force in the detaching blow, the bulb of percussion can be very pronounced. The bulb is the result of the compression of the rock due to impact, and it is the elastic rebound from this compression that actually detaches the flake from the core.

Ripples

Ripples can often be observed on flakes made of obsidian and other very fine-grained materials. These radiating waves in the stone are actually deformations of the rock resulting from the shock wave that accompanied the detaching blow. They look like frozen ripples on a pond after a pebble has been tossed into it.

Hatchure Lines

Hatchure lines occur in flakes where extreme force was used in their removal from the core. The lines are actually hairline cracks resulting from interference shock waves bouncing around within the rock before the flake actually detaches itself. In the most extreme cases, these interfering shock waves can actually cause the flake to shatter as it is being detached.

Basic Techniques

There are four basic techniques that have been employed in the manufacture of stone tools. These four techniques are:

1. Hammer and Anvil
2. Bipolar
3. Hard Hammer
4. Soft Hammer

The following sections will explain each of these techniques in turn.

Hammer and Anvil Technique

The hammer and anvil technique for removing flakes from a core is perhaps one of the oldest documented methods. It is quite effective for making large flakes for direct use as tools, or for use as blanks from which shaped tools can be made. This technique entails using the core as a hammer, and striking the edge of the core against a large, stationary rock (the anvil) in order to remove a flake.

There are a number of disadvantages to the technique, however. The principal disadvantage is that the flintknapper does not have a great deal of control over the flake removal process. A second disadvantage is that the flakes removed in this manner fly up and away from the anvil, becoming very dangerous projectiles for anyone standing nearby.

Bipolar Technique

The bipolar technique is a modification of the hammer and anvil technique. In bipolar flaking, the core is placed on the anvil for support, and then struck with a large heavy hammer. The compression from both ends of the core cause it to shatter into hundreds of flakes, some of which will be large enough, and of the right shape for use as tools. This technique is often found in areas where the only reliable source of workable stone is rounded river cobbles that are extremely hard to work in any other fashion.

The principal disadvantages to the bipolar technique are that there is very little control over the flake making process, and it wastes a great deal of raw material to get a few usable flakes.

Hard Hammer Percussion Technique

Both of the techniques already discussed depend on percussion to remove a flake from a core. Hard hammer percussion, as the name implies, relies on the same principles, but provides more control over how the flake is detached. In hard hammer flaking, the core is held in one hand, and struck with a hammerstone. Technically, the hammerstone must be made of a material that is harder that the core material so that it does not shatter in the flintknapper's hands. By using hard hammer percussion, the experienced flintknapper has very good control over where the flake will be detached and the size of the flake.

Soft Hammer Percussion Technique

While both hard and soft hammer methods take advantage of the fact that cyrptocrystalline rocks all break according to the Hertzian Cone principle, soft hammer percussion adds an added dimension of control to the process. In soft hammer flaking, a hammer or baton of material softer that the core is used. This could be soft limestone, deer antler, bone, or hardwood. Striking the core with the baton initiates a fracture according to the cone principle, but the soft hammer material tends to catch the edge of the flake, allowing the experienced flintknapper to actually help pull the flake off of the core. This works because the stone is actually shearing or tearing, rather than shattering, so it is a controlled breakage process.

Pressure Flaking Technique

Pressure flaking is used for the final trimming and sharpening of the edges of stone tools. It is also often the method employed to sharpen tools during their use-life. Generally, pressure flaking is done with a durable, flexible tool such as a piece of antler tine. The technique takes advantage of the elasticity of the stone to actually peel thin flakes off of the core material. The more elastic the material, the better it is for pressure flaking. Thus, the finest examples of long, thin pressure flakes come from obsidian specimens.

Department of Anthropology, UCSB

Brian M. Fagan and George H. Michaels

All contents copyright © 1996, The Regents of The University of California. All rights reserved.
Revised: January 29, 1996