The basic assumption behind the technique of high power microwear analysis
is that contact between the flint tool and a specific material like wood,
will produce a polish which is distinct from that produced by contact with
some other material like bone. This assumption has come into question (Newcomer,
Grace and Unger-Hamilton 1986). The failure to identify specific wood,
bone, antler etc. polishes in blind tests (Unrath
et al. 1986), has demonstrated that, rather than being distinctive,
these polishes overlap to the extent that they represent a continuum, not
discreet recognisable entities. This lack of distinctiveness has been further
demonstrated by texture analysis, using image processing techniques, which
involves the measurement of the differences between polishes created on
tools by contact with various materials by mathematically characterising
the textures of the polishes. These techniques and the results of the texture
analysis were presented in the previous chapter.
In response to the fundamental doubts that have been raised about the accuracy
and usefulness of microwear analysis as it is currently practiced, a new
approach which attempts to standardise the methodology of microwear analysis
and to test the limits of its interpretations has been developed. The method
involves the systematic recording of the functionally diagnostic attributes
of a tool. These attributes are described using a standard vocabulary and
the descriptions can be replicated enabling different analysts to describe
the same tools in similar ways. Correlations between the variables then
allow the analyst to eliminate some of the possible functions of a tool
until the most probable function is isolated. In some cases the elimination
of possible functions leaves only one that is consistent with all the wear
traces on the tool. This means that functional reconstructions which include
the specific material the tool was used to work can be postulated with some
confidence.
Other analysts describe polish characteristics in terms of smoothness, brightness
and such features as comet shaped pits, claiming that there is general agreement
about the characteristics of particular polishes. However a comparison of
different workers' characterisation of the polish left by working bone,
for example, show considerable disagreement; one describes bone polish as
bright, rough with micropits less than 1 µm. in diameter (Keeley
1980,43), another as rough with depressions between 10-20 µm. in
diameter (Anderson-Gerfaud 1981 v.1,
58). Further descriptions of bone polish are matt, bright, rough or smooth
with depressions (Moss 1983, 92),
and finally as bright, rough or smooth with micropits, depressions and comet
shaped pits (Vaughan 1981, 140).
Thus bone polish can be rough or smooth, matt or bright, with micropits
or depressions or both, and there seems to be no real agreement about the
precise appearance of a distinctive bone polish. Gendel
and Pirnay (1982) state that their smooth bone polish clearly resembled
Keeley's smooth antler polish, and so made no attempt to distinguish between
bone and antler as worked materials.
Microwear analysts do use information other than polish characteristics
in their functional reconstructions of tool use, but this usually takes
the form of supportive evidence for determining the motion of the tool.
Gendel and Pirnay (1982) in their
publication of the results of a blind test, state that they rely principally
on the distinctive nature of polishes but also that "Inferring the
method of use involves the consideration of several factors other than the
distinctive quality of the microwear polishes. These include the morphology
of the working edges, utilisation damage, the orientation of striations
and the location and extent of microwear polishes" (ibid, 252). They
do not however, present this information is a detailed or systematic way.
In addition they note specific features as diagnostic of worked materials.
For example, the two dry hide working tools in their test were identified
by the presence of rounded edges and short striations. In experiments conducted
at the Institute on dry hide these features are not always present and so
cannot be assumed to have a direct correlation with a specific material.
The approach to use-wear analysis employed here does not rely on any single
variable being diagnostic, but on the agreement of all the variables which
lead to a logically consistent functional reconstruction. High power microwear
analysis proceeds on the assumption that distinctive polishes are produced
by working different materials, hence bone polish, hide polish etc. The
approach presented here is based on a model of polish development as a continuum,
and no attempt is made to assign a polish as material specific.
The theory behind polish development began with a model of distinctive,
material specific polishes (Figure 30). This has been demonstrated to be
too simple by the repeated failure of analysts to recognise these distinctive
polishes consistently and so the model has been modified. It has been accepted
that all materials produce the same polish during the early stages of tool
use, and then as work progresses the polishes develop separately, though
overlapping does occur as in Figure 31 (after Vaughan
1985, 46).
The failure in blind tests to discriminate between these polishes (Newcomer
et al. 1986, Unrath et al. 1986)
and the results of the texture analysis of microwear polishes (Grace
et al. 1985) indicates that the real situation is that the overlapping
of polish types is far greater, as illustrated in Figure 32.
Consequently a model of polish development as a continuum has been adopted.
The important variables of this model are the hardness of the worked material
and the duration of use, therefore the model illustrated in Figure 33, is
proposed.
In this model polish develops as a continuum until the used area is completely
polished with no unused flint texture remaining. The shape of the curve
is determined by the hardness of the worked material so that flints that
have been used on bone will develop polish more rapidly that polish produced
by working a softer material such as hide. This means that a particular
level of polish development observed by an analyst (such as X in
Figure 34) may be produced by, for example, use on bone for 6 minutes, antler
for 11 minutes, wood for 14 minutes or hide for 27 minutes.
The fact that the duration of tool use is unknown with archaeological
material, means that polish X could be the result of working any
of these different materials. Therefore the model used in conjunction with
this approach is to treat polish as a single continuum as in Figure 35.
The reasons for adopting this model are that until more research has
demonstrated the precise mechanism of polish formation and development,
it is preferable to use the simplest explanation that concurs with the observed
data (employing Ockham's Razor). If further research allows for a more precise
model that is helpful in interpreting the function of stone tools then the
model will be modified accordingly.
The following explanation of the multi-dimensional approach to use-wear
analysis is divided into sections that deal with the different aspects of
the method.
SECTION 2 deals with the procedures for cleaning the flints used in conjunction
with this method.
SECTION 3 deals with the practical aspects of using microscopes for use-wear
analysis and the photographic recording of polish images.
SECTION 4 explains how the observations are recorded.
SECTION 5 defines the variables and their values and describes how the values
are measured.
SECTION 6 discusses the functional significance of the variables. The definition
and measurement of the variables are separated from the discussion of their
functional significance so that SECTION 5 may be used as a manual for observation
recording. It is important that observations are separated from interpretation.
If these two aspects are not carefully delineated they can often be confused,
so that the reader is not sure if he is dealing with an observation or an
interpretation of an observation.
SECTION 7 describes the process of interpretation and the way in which attributes
are combined to eliminate motions of use and worked materials until the
most probable function can be interpreted. Also, Section 7 includes the
definitions of the different motions of use that are employed in this method.
SECTION 8 gives examples of tools whose function have been interpreted by
this method in blind tests.
SECTION 9 describes the role of experimental replication of the function
of tools that is an integral part of this method.
SECTION 10 describes the blind test used to assess the usefulness of this
method and contrasts it with previous blind tests.