Lithic reduction
Lithic reduction involves the use of a hard hammer precursor, such as a hammerstone, a soft hammer fabricator (made of wood, bone or antler), or a wood or antler punch to detach lithic flakes from a lump of tool stone called a lithic core (also known as the "objective piece"). As flakes are detached in sequence, the original mass of stone is reduced; hence the term for this process. Lithic reduction may be performed in order to obtain sharp flakes, on which a variety of tools can be made, or to rough out a blank for later refinement into a projectile point, knife, or other object. Flakes of regular size that are at least twice as long as they are broad are called blades. Lithic tools produced this way may be bifacial (exhibiting flaking on both sides) or unifacial (exhibiting flaking on one side only) .
Cryptocrystalline or amorphous stone such as chert, flint, obsidian, and chalcedony, as well as other fine-grained stone material, such as rhyolite, felsite, and quartzite, were used as a source material for producing stone tools. As these materials lack natural planes of separation, conchoidal fractures occur when they are struck with sufficient force. The propagation of force through the material takes the form of a Hertzian cone that originates from the point of impact and results in the separation of material from the objective piece, usually in the form of a partial cone, commonly known as a lithic flake. This process is predictable, and allows the flintknapper to control and direct the application of force so as to shape the material being worked.
Removed flakes exhibit features characteristic of conchoidal fracturing, including striking platforms, bulbs of force, and occasionally eraillures (small secondary flakes detached from the flake's bulb of force). Flakes are often quite sharp, with distal edges only a few molecules thick, and can be used directly as tools or modified into other utilitarian implements, such as spokeshaves and scrapers.
Techniques
Percussion reduction
Percussion reduction, or percussion flaking, refers to removal of flakes by striking a core or other objective piece, such as a partially formed tool, with a hammer or percussor. Alternatively, the objective piece can also be struck against a stationary anvil-stone, known as bipolar percussion. Percussors are traditionally either a stone cobble or pebble, often referred to as a hammerstone, or a billet made of bone, antler, or wood. Often, flakes are struck from a core using a punch, in which case the percussor never actually makes contact with the objective piece. This technique is referred to as indirect percussion. [1]
Hard-Hammer percussion
Hard hammer techniques are generally used to remove large flakes of stone. Early flintknappers and hobbyists replicating their methods often use cobbles of very hard stone, such as quartzite. This technique can be used by flintknappers to remove broad flakes that can be made into smaller tools. This method of manufacture is believed to have been used to make some of the earliest stone tools ever found, some of which date from over 2 million years ago.[2]
It is the use of hard-hammer percussion that most often results in the formation of the typical features of conchoidal fracture on the detached flake, such as the bulb of percussion and compression rings [3]
Soft-Hammer percussion
Soft-hammer percussion involves the use of a billet, usually made of wood, bone or antler as the percussor. Flakes produced in this manner are generally smaller and thinner than those produced by hard-hammer flaking; thus, soft-hammer flaking is often used after hard-hammer flaking in a lithic reduction sequence to do finer work.[4]
In most cases, the amount of pressure applied to the objective piece in soft-hammer percussion is not enough for the formation of a typical conchoidal fracture. Rather, soft-hammer flakes are most often produced by what is referred to as a bending fracture, so-called because the flake is quite literally bent or "peeled" from the objective piece. Flakes removed in this manner lack a bulb of percussion, and are distinguished instead by the presence of a small lip where the flake's stiking platform has separated from the objective piece. [5]
Pressure flaking
Pressure flaking is a method of trimming the edge of a stone tool by removing small lithic flakes by pressing on the stone with a sharp instrument rather than striking it with a percussor. This method, which often uses punches made from bone or antler tines (or, among modern hobbyists, copper punches or even nails), provides a greater means of controlling the direction and quantity of the applied force than when using even the most careful percussive flaking. Usually, the objective piece is held clasped in the flintknapper's hand, with a durable piece of fabric or leather protecting the flintknapper's palm from the sharpness of the flakes removed. The tip of the flaking tool is placed against the edge of the stone tool and pressed hard, removing a small linear or lunate flake from the opposite side. In some instances, a hammer and punch is used while the tool is held down with a vice. The process also involves frequent preparation of the edge to form better platforms for pressing off flakes. This is usually accomplished with abraders made from a coarse-grained stone such as basalt or quartzite. Great care must be taken during pressure flaking so that perverse fractures that break the entire tool do not occur. Occasionally, outrepasse breaks occur when the force propagates across and through the tool in such a way that the entire opposite margin is removed.[6]
The use of pressure flaking facilitated the early production of sharper and more finely-detailed tools. Pressure flaking also gave toolmakers the ability to create notches where the objective piece could be bound more securely to the shaft of the weapon or tool and increasing the object's utility.
Thermal fracturing
One of the biggest myths about lithic reduction is the ability to remove flakes using thermal fracturing. According to the myth, thermal fracturing is a technique which uses thermally induced stress fractures to remove flakes. Supposedly used for finishing a tool, the stone is first heated and then drops of water or saliva are dripped on to the edge. When the area touched by the water rapidly cools, it causes stress fractures and the material either spontaneously flakes or partially cracks allowing further removal using light pressure. In reality however, when a stone is heated and then quickly cooled by applying liquid, the tool may fracture completely or not respond at all. Reheating generally causes the stone tool to erode and eventually fall apart. In some cases, the tool undergoing this treatment explodes due to thermal shock potentially injuring the tool-maker. In any case, it is not possible to predict the size and direction of the fracture. It is thought the myth may have originated as a joke at the expense of an early anthropologist describing native methods of the manufacture of stone projectile points.
See also
Further reading
References
- Andrefsky, W. (2005) Lithics: Macroscopic Approaches to Analysis. Cambridge: Cambridge University Press. ISBN 0521615003
- Cotterell, B. and Kamminga, J. (1987) The Formation of Flakes. American Antiquity 52:675-708
