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Pre-Columbian Peruvian Metals
Sample 16
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Weaving tool with cotton thread
Moche
North Coast, Peru
ca. 100-600 AD
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Report by :
Kevin Elliott
May 15, 2003
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| Introduction |
Figure 1: Weaving tool with cotton thread
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The purpose of this study was to examine a Pre-Columbian Peruvian sample
possibly used as a weaving tool, and to determine the authenticity of
the sample (Sample 02-01-16). We were also interested in determining
the metal composition and forming techniques of the sewing tool. The
sample was found with white cotton resembling thread wrapped around
the back end. A picture of the sample is given as Figure 1.
Pre-Columbian Peruvian tribes wove textiles for use as rugs, clothes
and for ornamental purposes. Weaving was an important expression of
art incorporating intricate designs, often including a design within
a design, as well as complicated weaving methods such as going back
over a single stitch three times1. Pre-Columbian Peruvians wove using
functional yet simple tools resembling large needles often made of whatever
metal was available, primarily copper from the copper rich Andes.
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| Proceedure |
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| The first step of the procedure was to section off two pieces
of the sample in a way that damages the sample as little as possible.
It became necessary to view the sample in the cross-sectional and longitudinal
direction to detect any differences in microstructure revealing possible
working. The second step of this process was to mount, grind, polish the
sample. The sample was then etched in a chemical etch consisting of equal
parts of water, ammonia, and 3% hydrogen peroxide. After etching, the
microstructures of each direction were examined to offer clues to the
forming process. Next, a series of tests were taken to determine the hardness
of the sample to verify the forming method. Finally, an x-ray photograph
was taken of the specimen in order to aid determination of the specimen's
authenticity. |
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Figure 2: Cross-sectional view of the copper
microstructure showing annealing twins, deformation twins, and circular
inclusions.
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Figure 3: Longitudinal view of the copper microstructure
showing annealing twins, deformation twins and elongated inclusions.
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| Results and Discussion |
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| The sample is clearly of copper composition
when viewed without even the aid of a microscope. Copper has a very distinctive
color and a very distinctive blue-green pastel oxide color (as shown in
Figure 1). When viewed with a microscope, there are many tiny inclusions
visible that suggest that the metal was not perfectly pure. See Figures
2 and 3 for cross-sectional and longitudinal views of the copper microstructure.
The inclusions are most likely copper oxide or another unwanted material,
and this is very logical since the pre-Columbian Natives had limited means
of purifying metals. This lends credence to the argument that the sample
is authentic.
An analysis of both the cross-sectional and longitudinal views of the
tip show similar grain size in both direction but elongated inclusions
in the longitudinal direction. This leads one to believe that at least
the tip of the object was hammered after being annealed. Finally, the
presence of annealing twins and deformation twins can be used to determine
the forming technique for the sewing tool. The sewing tool was most
likely hammered from a cast copper rod while the copper was hot and
then put back into the fire to anneal the grains and make the sample
more workable. The annealing yields annealing twins, and the hammering
after recrystallization yields the deformation twins.
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Figure 4: X-Ray photograph of weaving tool.
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| Discussion (con't) |
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| Experimental evidence that the copper was cast,
hammered, annealed, and then hammered again to achieve a point on the
tip of the weaving tool lies within the microhardness for the sample.
The expected microhardness for a pure copper cold worked sample is between
100 and 120 Vickers2. The calculated microhardness for the copper sample
is 122.8 Vickers. This data is just outside the range of values for worked
copper, which can be justified due to the inclusions in the copper microstructure.
Additionally, values were calculated for the tip of the weaving tool which
was worked vigorously to make it into a point for weaving, thus a value
on the higher end of the range of values is to be expected.
The x-ray photograph taken of the specimen showed the specimen to be
of the same composition throughout the tool as evidenced by the same
color and shade for the entire tool. A fake sample made of a cheaper
material than copper and then copper plated would not look so homogeneous
when viewed in the x-ray spectrum. See Figure 4 for an x-ray photograph
of the sample. A final way to determine the specimen's age and therefore
authenticity, would be to carbon date the thread attached to the end
as seen in Figure 1. C-14 dating of the tread, showed the tread to date
between 1500-1650 which would date the piece much later than anticipated
(figure 5).
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