Microscopic inspection of artifacts can be conducted on tools and debitage to evaluate how the artifact was used. Lithic tool functions using ‘microscopy’ are understood at different scales of interpretive detail. Some forms of microwear analysis interpret tool function as type of action (scraping, slicing, chopping, etc.). Other types of microwear analysis attempt to interpret tool functions in more detail, such as the type of material being worked (bone, hide, flesh, etc.). Each of these different scales of interpretive detail come with different levels of confidence in their accuracy, and in some cases are dependent upon the type of microscopy equipment employed by the investigator.
Most researchers recognize three kinds of magnifying equipment used for microwear analysis; ‘scanning electron microscope’ (SEM), ‘metallurgical microscope’, and the ‘stereomicroscope’. The SEM captures an image with a controlled electronic field and is effective at over 10 000 x magnification. Magnification at this level may not recognize larger evidence of wear such as breakage patterns on the edge of the tool. The metallurgical microscope is useful for magnification of objects in the 100-500x range. These microscopes use incident lighting that illuminates objects from above at a 90° angle. Stereomicroscopes are effective in the range of approximately 6-150 x magnifications and use external lighting. There are advantages and disadvantages to each microscope, ranging from equipment cost, to amount of time required for analysis, to appropriate scale of resolution.
In general, three kinds of wear have been recognized by microscopy techniques in lithic analysis; ‘striations’, ‘polishes’, and ‘microchipping’. Striations result from the contact of the worked material and the tool and it occurs when debris is introduced during the operation of the tool, resulting in scratches (striations) on the tool surface. Polishes are produced by abrasion and deposition of silica on the stone tool. Silica is often deposited as a result of working materials such as wood from which silica is displaced and transported to the tool surface. Striations and polishes are best viewed under high magnification with either a metallurgical microscope or with the SEM. Microchipping is caused by the contact between the tool edge and the material being worked. Different patterns of microchipping are produced by different actions of tool use and by the relative density of material being worked. The stereomicroscope is effective for recognizing various patterns of microchipping damage.
Microwear analysis of lithic artifacts is influenced by a wide variety of variables that make tool functions challenging to interpret. For instance, the type of stone a tool is produced from is known to break differently under similar kinds of stresses or impacts. This means that stone type may have different kinds of chipping damage when performing the same kinds of tasks. The edge angle of the cutting tool will also influence the size and amount of chipping damage. Similarly, the angle and direction of the tool to the worked surface also adds variability to the wear pattern. Tools from archaeological sites have the added problem of postdepositional wear such as trampling, erosion, and weathering.
Researchers often switch from one microscope to another while conducting lithic analysis. For instance, a stereomicroscope might be used initially to scan the artifact surface for evidence of use.
Once detected, the location on the artifact with evidence of use might be greatly magnified in search of polishes, striations, or debris. Since different artifact assemblages are composed of different kinds of raw materials and different kinds of weathering contexts, microwear analysis of excavated lithic artifacts is often conducted in unison with experimental studies using materials gathered from the same region or from the same raw material source. Experiments such as making cutting tools and cutting or slicing different kinds of plants and animal parts are conducted to establish a control sample for comparison against the excavated artifacts.
See also: Blood Residue Analysis; Chemical Analysis Techniques; Phytolith Analysis; Starch Grain Analysis.
World History
