The Impact of Ceramic Raw Materials on the Development of
Hopewell and Preclassic Maya Pottery
A Thesis submitted to the
Graduate School
of the University of Cincinnati
in partial fulfillment of the
requirements for the degree of
Master of Arts
in the Department of Anthropology
of the College of Arts and Sciences
by
Dominique Sparks-Stokes
May 2019
B.A. University of Cincinnati
December 2017
Committee Chair: Kenneth Barnett Tankersley, Ph.D.
ABSTRACT
This thesis examines the role ceramic raw materials play in the technological development of pottery in two geographically separated regions, the Middle Woodland Hopewell in the Ohio
River Valley and the Preclassic Maya in Lowland Belize. To this end, a suite of physical, mineralogical, and chemical analytical techniques including scanning electron microscopy, energy dispersive spectrometry, X-ray fluorescence spectrometry, and X-ray diffractometry is used to examine the ceramic raw material composition of pottery sherds from the Hopewell Twin
Mounds Village site in southwestern Ohio and the Preclassic Maya Colha site in northeastern
Belize. The Preclassic Maya pottery from the Colha site is technologically more advanced than
Hopewell pottery from the Twin Mounds Village site in terms of hardness, porosity, and refractory properties such as thermal conductivity, resistance to thermal shock, and thermal decomposition. These ceramic properties result from the use of locally available volcanogenic clays at the Colha site. Comparable ceramic raw materials were unavailable to the Hopewell at the Twin Mounds Village site, which resulted in poorer quality pottery.
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ACKNOWLEDGMENTS
The Court Family Foundation and the Charles Phelps Taft Foundation supported this project. Dr.
Fred Valdez, University of Texas, Austin provided pottery sherds from the Colha site in Belize, which was imperative to the completion of this work. Many thanks go to Department of Geology and Dr. Warren Huff for use of their instruments and assisting with X-ray Diffractometry analysis and Liquid separation. Gratitude goes to my loving friends and family for both mental and emotional support as I partook though this journey. The guidance and encouragement of Drs.
Kenneth Barnett Tankersley and Sarah Jackson made this thesis possible.
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TABLE OF CONTENTS
Abstract……………………………………………………………….……….….….ii
Listing of Figures…………………………………………………….………...…...vii
Listing of Tables………………………………………………………………….....ix
Chapter 1: Introduction………………………………………………………………1
Chapter 2: Physical Properties of Pottery………………………...………………….7
Physical Properties of Clay…………………………………………………..7
Physical Properties of Pottery.……………………………………….….....10
Hardness………….…………………………………………….……....…..10
Strength……………………...…...…….………………..………….………11
Porosity…………. ……………………………………………….……...... 12
Color……………………………...…….……………………….……...…..12
Firing Temperature………………………………………….……………...13
Texture…………….………………………………………….………....….14
Summary..………………………...…….………………….…………...…..15
Chapter 3: Archaeological Sites………….………………………………………...16
Colha……..…………………...…………………………….………………18
Twin Mounds……………………………………………….………………20
Summary…………….. ……..……………………………….……………..23
Chapter 4: Methods and Analyses..….…………………...……….…………...…...24
Pottery Sample………..…...……………………………….…………..…...25
Physical Properties….……..………………...………………………....…...25
Sample Preparation..………………………………………….…………….25
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Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometry
(EDS)…………………………...…….……………………………….…....29
Powder X-ray Diffraction Analysis (XRD)....…………….……….…….....30
Energy Dispersive X-Ray Fluorescent Spectrometry (ED-XRF)………...... 30
Summary…………………………...…….………………….………….…..31
Chapter 5: Results……….…………………………………..………...……….…...32
Scanning Electron Microscopy (SEM)………………..…….……………...32
Energy Dispersive Spectrometry (EDS)……………………..………...…...34
X-ray Diffractometry Analysis (XRD).……………….………….…...…....35
Energy Dispersive X-ray Fluorescent Spectrometry (ED-XRF).…………..38
Summary………….…………………………………………………....…...41
Chapter 6: Discussion and Conclusion.………..…………………………….……..42
References Cited………………………………………………………..……….….45
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LIST OF FIGURES
Figure 1: The geographical locations of the Middle Woodland Hopewell Twin Mounds
village and Preclassic Maya Colha site.
Figure 2: The geologic setting of the Preclassic Maya Colha site relative to the source of
volcanogenic clays (after Tankersley at al., 2011, 2016).
Figure 3: The geologic setting of the Twin Mounds site relative to ceramic raw material
source areas (after Dalby, 2007).
Figure 4: Middle Woodland Hopewell pottery sherd sample from the Twin Mounds village
site.
Figure 5: Preclassic Maya pottery sherd sample from the Colha site.
Figure 6: Photomicrographs of quartz, calcite, and clay minerals in sherds from the Colha
site.
Figure 7: Photomicrographs of quartz, calcite, and clay minerals in sherds from the Twin
Mounds village site.
Figure 8: SEM micrographs of temper raw materials from Hopewell pottery sherds
from the Twin Mounds Village site.
Figure 9: SEM micrographs of temper and paste raw materials from Preclassic Maya pottery sherds from the Colha site.
Figure 10: XRD analysis of Hopewell pottery sherds from the Twin Mounds village site.
Figure 11: XRD analysis of ceramic raw materials from the vicinity of the Twin
Mounds village site.
Figure 12: Mineralogical composition of clay minerals at the Twin Mounds Village site.
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Figure 13: XRD analysis of ceramic raw materials from the vicinity of the Colha site (after
Tankersley et al., 2011, 2016).
Figure 14: XRD analysis of Preclassic Maya pottery sherds from the vicinity of the
Colha site.
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LIST OF TABLES
Table 1: Radiocarbon dates obtained from the Colha and Twin Mounds Village sites.
Table 2: Physical properties of Preclassic Maya and Middle Woodland Hopewell pottery
sherds.
Table 3: EDS analysis of Hopewell pottery sherds from the Twin Mounds village site.
Table 4: EDS analysis of Preclassic Maya pottery sherds from the Colha site.
Table 5: XRF analysis of major elements in Hopewell pottery sherds from Twin Mounds
village site and Preclassic pottery sherds from the Colha site.
Table 6: XRF analysis of pottery sherds from Twin Mounds village and Colha sites.
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Chapter 1: Introduction
In 1959, Leslie White published a paradigm shifting anthropological theory in The Evolution of
Culture: The Development of Civilization to the Fall of Rome. Like its human biological counterpart, White believed that non-genetic culture also evolves. A primary aspect of his theory was the technological component of culture. He argued that technology was the driving force behind cultural evolution. White emphasized that the material, physical, and chemical aspects of technology provide humans with a means of survival and ultimately adaptation.
White’s theory of cultural evolution drew upon the economic theoretical framework of
Marxian economics. In particular, White focused on concept that the economic base determines the superstructure of society (i.e., political power structures, roles, state, etc.). In this perspective, the role of ceramic technology can be viewed as an important facet of a culture’s economic base, which in part determines the development of social superstructure.
Ceramic raw material availability, quality, and their physical properties and chemical composition ultimately limit the level of the technological development of pottery.
Consequently, the origin of pottery and its level of development vary in many parts of the world and at different points in times (Brown, 1989). Therefore, it is not surprising that the level of ceramic development corresponds to the level of a culture’s polity. That is, complex levels of ceramic technology are associated with more complex polities.
Cross-culturally and pan-globally, the earliest pottery co-occurs with plant domestication and the need to store grain in insect-free containers. Food storage in ceramic containers was a crucial technological adaptation to increasing populations in environmentally or socially circumscribed regions. These subsistence and demographic changes are found in ceramic
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technological innovations, class differences, and demands on labor (Goody, 1982:50153). Thus,
understanding changes or differences in the development of ceramic technology are important
indicators of changes in ancient subsistence economies (Barnett and Hoopes 1995; Mills, 1999;
Arnold, 1999; Skibo and Blinman, 1999).
With higher quality ceramic raw materials, greater technological developments could be
made. In these situations, pottery played multiple and more complex roles in societies that went
far beyond their subsistence functions. In complex polities, high-quality ceramic raw materials
allowed pottery to enter exchange networks and became modes of social communications. Their
new and differentiated roles in social communication were possible because of the physical and chemical properties of the ceramic raw materials (Stark, 1999). The accessibility and procurement of higher quality ceramic raw materials facilitated a shift from functional mundane pottery to elaborately decorated vessels in a structural hierarchy and status symbols in a complex polity, which communicates social strata, sacred values, and economically valued prestigious gifts (Stark, 1999).
Anthropologically, the economics of ceramic production can be viewed as the
cornerstone of the human livelihood in complex polities. In other words, understanding the modes of ceramic production is vital to our understanding of complex forms of social and
political organization (Longacre, 1999). If the level of a culture’s polity is correlated with the
level of ceramic technology and the level of ceramic technology is limited by the physical and
chemical properties of ceramic raw materials, then we would expect to find cultural areas that
were advantaged while other areas were disadvantaged in regards to the rate and level of ceramic
development. Understanding the levels of ceramic development and its role in the rise of
complex societies is of more than a little anthropological interest (Rice, 1996; Skibo, 1999).
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Archaeologists have used a variety of approaches to look at the relationship between the development of ceramic technology and complex polities (Longacre, 1999). Bronitsky (1986) suggested a materials science approach to examination this relationship. He was inspired by the likes of Shepard (1956), Matson (1965), and Braun (1983). More recently Kingery (2001), Tite
(1999, 2008), and (Skibo, 2013) have also investigated the physical and chemical properties of pottery to better understand ceramic technological development and social and cultural complexity.
Previous archaeological positions have assumed that the technological development of pottery was based solely on the evolutionary stage of culture rather than the local availability and quality of ceramic raw materials. Given the spatial distribution and geological variation of clay minerals, it is likely that some ancient cultural areas had higher quality ceramic raw materials than others, which would have advantaged and hastened or disadvantaged and stifled the technological development of pottery. One effective way to evaluate this working query is to compare the availability of ceramic raw materials with the chemical and mineralogical composition of ancient pottery from known temporal and cultural contexts from geographically distant areas (Bronitsky, 1986). In this vein, determining the mineralogical and chemical composition of ceramic raw materials is a fundamental aspect of studying archaeological pottery
(Griffiths, 1999).
Pottery is especially important to polities that are sedentary or with lower mobility than foragers. In these social and political settings, pottery making is both widespread and produced in high volume. Thus, it has been used as an indicator of cultural progression and technological development. Furthermore, pottery is relatively resistant to chemical decomposition and mechanical disintegration (Freestone and Gaimster, 1997; Griffiths, 1999). Before the advent of
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absolute dating methods such as radiocarbon dating, seriating pottery provided archaeologists
with a way to compare technological developments between ancient cultures. During the 19th
century pottery was organized into sequences according to assumed stylistic changes and
frequency of appearance through time. These changes in ceramic production were used as a way
to develop a relative chronology. Rather than focusing on ceramic raw material composition,
archaeologists have historically concentrated on developing pottery typologies based on stylistic
traits. These ceramic typologies have been used as the basis of artifact assemblages, which have
been ordered to define archaeological traditions from a region or locality (Shepard, 1956;
Whittaker et al., 1998).
Archaeologists have used typological variations in pottery to define developmental
ceramic series. The sequence of these ceramic types is theoretically chronological, but requires
independent chronometric assessments. Such typologies have by and large ignored or excluded
the mineralogical and chemical properties of ceramic raw materials. Although drawing
conclusions based on the appearance of pottery styles, types, and assemblages is still useful, methods of analyses that identify sources of ceramic raw materials have become important when
looking at the bigger picture of pottery production and cultural evolution (Griffiths, 1999).
In this thesis, I seek to explain how ceramic raw materials are related to the level of
technological development of pottery in certain ancient societies. Previous archaeologists have
described the cultural level of ceramic development and the character of ceramic technologies in
in terms of how people maintain, specialize, and innovate pottery differently (c.f., Shepard 1956;
Matson 1965; Braun 1983). However, this traditional archaeological perspective fails to address
the roles of how raw material availability and quality play out in terms of ceramic technology
and development. While the focus of this thesis is on the Western Hemisphere, this same line of
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inquiry is applicable to ancient ceramic production in any location in the world.
This thesis examines the ceramic raw material composition of two contemporary (~2,000
B.P.), but geographically separated archaeological cultural complexes—the Middle Woodland
Hopewell cultural complex in the Ohio River valley and the Preclassic Maya in Belize. The basic
units of analysis used for this project include the mineralogical and chemical composition of the
paste and temper used to manufacture pottery at the Preclassic Maya site of Colha in Belize and
the Middle Woodland, Hopewell component of the Twin Mounds village site in the Great
Miami-Ohio River confluence area of Ohio (Valdez, 1987; Tankersley and Haines, 2010). These
cultural areas were selected as case studies because the pottery samples come from stratified,
well documented, and chronometrically dated contemporaneous contexts. The issue of
contemporaneity is significant because each cultural area exhibits a dramatically different level of ceramic technological development.
In the following chapter, I discuss how archaeologists have defined the physical
properties of ancient pottery including temper, paste, hardness, strength, porosity, color, firing temperature, and texture. I then review the geographic and geologic settings of the Preclassic
Maya Colha and Hopewell Twin Mounds village archaeological sites as well as the history of investigations at these sites. In my methods and analyses chapter, I provide my sample size and the physical properties of the sample as well as how I prepared samples for scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), powder X-ray diffraction (XRD) and energy dispersive X-ray fluorescent spectrometry (ED-XRF). This chapter is followed by the results of these analyses including a presentation of photomicrographs of Preclassic Maya and
Middle Woodland Hopewell paste and temper together with the percent mineral and chemical content and the trace element content. Finally, I draw conclusions based on these analyses and
5 discuss the results of these data in terms of the role ceramic raw material played in the development of ancient Presclassic Maya and Middle Woodland Hopewell pottery.
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Chapter 2: Physical Properties of Pottery
Archaeologists use a suite of physical properties to classify prehistoric ceramics. These physical properties result from the mineralogical and chemical composition of the ceramic raw materials used in the construction of pottery. The mineralogical and chemical composition of ceramic raw materials in turn determines the quality of pottery, which was produced by ancient potters. In this chapter, I will be describing the physical properties of clay and pottery and explain how they are measured.
Physical Properties of Clay
Understanding the origin of ceramic raw materials (i.e., paste and temper) is crucial to our understanding of the culture of potters (Shepard, 1956). Ceramic raw materials provide a baseline of knowledge that can be used to make meaningful cultural inferences about a culture’s ceramic production (Shepard, 1956). In the case of the Preclassic Maya and Hopewell, pottery is
both an art form and a specialized craft that is used for everyday life (Longacre, 1991).
Before it is decorated or personalized, raw clay has to be collected and processed into a
paste and mixed with temper. Together, paste and temper determine the strength, durability,
porosity, and, to an extent, the luster of pottery. Their physical and chemical properties control
how pottery can be fired and the way it can be formed, molded, or cast (Shepard, 1956;
Longacre, 1991).
Temper is a non-plastic material added to the clay, which plays a significant role during the manufacturing, drying, and firing components of making pottery (Shepard, 1956; Longacre,
1991). Archaeologically, the individual non-plastic and plastic elements of pottery can be very
minute particles that cannot be distinguished by the naked eye. When mixed with water, they
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produce a tacky substance that can be molded to have shape and form. The temper creates a
polarizing binding and structure in the paste, and it plays a major role in the strength or weakness
of the vessel. Some tempers can make pottery more durable than others. A more durable temper
makes pottery stronger, but a large quantity of temper can make the pottery weaker and too
porous for use.
In the construction of pottery, as an art form or as a fundamental tool for use, there are
basic physical and chemical properties that are required for the formation and structural integrity
of a vessel. Thus, understanding the physical and chemical properties of pottery is crucial to our understanding of the ceramic technological development of ancient cultures. Pan-globally and
through time, ancient cultures collected and processed natural clay resources such as shale and
lacustrine deposits for the manufacture of paste (Tankersley and Meinhart, 1982; Tankersley and
Haines, 2010).
The source and quality of ceramic raw material sources are one of, if not the biggest,
determinates of the quality of pottery production. Ceramic raw materials include clay, temper,
and water. Ideal clay sources are bedrock shale or lacustrine deposits that can be easily turned
into a sticky fine-grained paste that becomes plastic or moldable when wet. Temper is the non-
plastic mineral or organic inclusions that are either found naturally in clay or deliberately added
to help make clays more workable and to limit shrinkage. Water is added to the mixture of clay
and temper to make pottery more plastic and easy to form into vessel shapes. Water evaporates
during both the drying and firing process (Sinopoli, 1991).
The quality of clay sources is defined by their origin (bedrock or lacustrine), particle size
(coarse to fine), mineralogy (chlorite, illite, smectite, etc.), and chemical composition (Ca, Fe,
Mg, Mn, etc.). Most commonly, particle size is considered the single most important physical
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trait when it comes to making paste. Ideally, the paste should have a very fine texture, which
means the particle size of clay must be less than two-thousandths of a millimeter (i.e., 2
microns). High quality paste takes on the ability to be easily malleable, hold shape when water is
added, and create thin vessel walls (Tankersley and Meinhart, 1982).
Clay sources are defined as primary or secondary. Primary clays occur as shale, a fine- grained sedimentary rock composed of one or more clay minerals with a fissile and laminated texture. Secondary clay sources occur as lacustrine deposits that are not lithified. They form in
the bottom of deeply ponded water, which results from a stream depositing fine-grained
sediments into the bottom of a basin. Lacustrine deposits are very well sorted and characterized
by thin layers of clay minerals (Shepard, 1956; Sinopoli, 1991).
Both primary and secondary clay sources contain non-clay particles including organic
material, rock fragments, sand, and other elements from the biosphere. Unless these particles are
removed from the clay, or allowed to remain in the clay as temper, they will have a direct impact
on how clay behaves in the production (workability), and drying, firing, and cooling (shrinkage)
of a ceramic vessel. Potters often add dissimilar materials to natural clays in order to enhance
and modify these characteristics. Some materials commonly used as temper include ash,
limestone, mica, and sand or organic materials such as chaff, seeds, or seed byproducts. Smaller
fragments of broken pottery, known as grog, may also be added to clay as temper (Sinopoli,
1991)
The raw materials, which were used by ancient potters for the manufacture of paste, were
not composed purely of clay minerals. Rather, ancient pastes contain other debris such as silt,
sand, organic materials, and rocks. These non-clay minerals would have had a major impact on
9 the characteristics of ceramic materials produced. Most notably, non-clay minerals directly affect the appearance, strength, porosity, hardness, and thermal resistance of pottery (Arnold, 1985).
Physical Properties of Pottery
Understanding the physical and chemical properties of pottery is important because it helps archaeologists classify and identify the culturally determined methods of manufacture. These properties can be used to cultivate a foundation for creating hypotheses about ancient cultural development and technology. Physical properties can be used to determine the conditions under which pottery is created. These properties include durability (hardness, porosity, and strength) and attractiveness (color, impacting by firing temperature, and luster). Ultimately, these properties have influenced the innovation of pottery throughout prehistory. Thus, interpreting how these properties are represented in ceramic artifacts is crucial to identifying the catalyst for innovation. The physical properties of pottery are a result of the mineralogical and chemical composition of the ceramic raw materials. Ultimately, they can be used to help decipher why the
Preclassic Maya pottery recovered from the Colha site in Belize was more technologically advanced than contemporary Hopewell pottery from the Twin Mounds Village site in the Great
Miami River valley of Ohio.
Hardness
Hardness is a physical property of pottery that is not measured by its ability to hold weight or withstand cracks. Rather, it is measured by a “scratch test,” using the Mohs Hardness Scale. This scale, named after Friedrich Mohs, a German mineralogist, was created in 1812. It compares the resistance of a ceramic surface being scratched by the sharp surface of ten reference minerals or
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materials of comparable hardness (1 Talc, 2 Gypsum, 3 Calcite, 4 Fluorite, 5 Apatite, 6
Orthoclase Feldspar, 7 Quartz, 8 Topaz, 9 Corundum, 10 Diamond). This scale is useful for
archaeology because it is objective, reliable, and provides a diagnostic property for pottery
surfaces. It compares pottery surfaces with a mineral of known hardness (Shepard, 1956;
Sinopoli, 1991).
Hardness is affected not only by firing temperature but also by impurities that render the paste more fusible. The fineness of grain, and density of the paste promote sintering, the process
of compacting and forming pottery by heating the paste without melting it to the point of
liquefaction. This process in turns depends upon the amount and kind of nonplastic materials as
it affects closeness of contact of the temper, the ease of sintering, and the firing atmosphere. To
that end, it acts on constituents of the paste and converts them to stronger fluxes (Shepard, 1956).
Archaeologically, hardness is a valued physical property if it is used in conjunction with others
properties such as strength (Shepard, 1956).
Strength
Strength is defined as the force required to fracture a ceramic vessel either part or whole.
Strength can be influenced by texture of paste, particle size, clay composition, method of
preparing the paste, technique of building the vessel, rate of drying, temperature, atmosphere of
firing, and shape and size of the vessel (Shepard, 1956). These conditions can determine the
nature of how the paste and temper bond to strengthen vessel construction. Strength is an
important physical trait because it affects the durability and use life of a vessel. Economically,
strength ensures the potter’s time spent to create the vessel was purposeful and cost effective.
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Tenacity, the resistance to breakage, is directly related to the use life for pottery (Pierce,
2005). Use life also depends on what the vessel was originally crafted for, how it is used,
serviced. Unlike the other physical properties, it is influenced by all other physical properties
such as hardness, paste composition, temper/paste ratios, and firing temperature, which making it
more complex and more sensitive (Shepard, 1956).
Porosity
Porosity is one of the most fundamental physical attributes of pottery. Porosity is the space
between the paste and temper before and after firing. These spaces are known as pores, which allow gases and liquids to pass throughout the vessel without breakage. The size and shape of these pores can influence the density and permeability of the vessel. Without porosity, pottery would break during the drying, firing, and cooling. Porosity increases the ability for a vessel to
withstand thermal shock. The porosity of pottery can be manipulated by adding more temper so it can withstand higher firing temperatures without shattering (Shepard, 1956). Porosity is measured by completely impregnating the pottery with water. This process compares the ratio of the mass of a dry sherd to the mass of a sherd in which all of the pores are filled with water
(Harry and Johnson, 2004).
Color
Archaeologists define pottery color using the semi-quantitative Munsell Soil Colors (Ruck and
Brown, 2015). This method is used because pottery is essentially an anthropogenic, meta-stable, metamorphosed soil. Munsell is a mathematical color system created by Albert H. Munsell to
provide an objective and reproducible way to define color quickly and accurately. The Munsell
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color system uses three attributes: (1) hue, a defined color term; (2) value, the lightness or
darkness of a color; and, chroma, the saturation or brilliance of a color. The color pottery results
from two major factors—firing and cooling (production) use (post-production). The components of production include the atmosphere, temperature, and duration of firing. Post-production involves anything done in lieu of construction, for example, what may occur after the vessel had
been manufactured such as washing, cooking, or being burned in a fire unintentionally (Shepard,
1956).
The stages of pottery manufacture have a significant influence in the color of the finished vessel. The clay minerals used to make the pottery may also affect color of pottery. For example, kaolinite alone produces the color white, illite and chlorite produce orange to red colors, and smectite produces a beige color. The firing atmosphere creates an environment in which the
pottery acquires additional coloring. For example, an excessive amount of oxygen produces
bright-oxidized colors. In a reduced atmosphere, oxygen is removed and reducing gases such as
carbon monoxide, hydrogen, and hydrogen sulfide produce dark colors and the deposition of
carbon known as smudging. If the atmosphere is variable, then portions of the pottery may be
vibrant and clear while other areas are darker and appear smokier. Thus, the color of pottery
reflects both the composition of the clay paste and conditions of the firing atmosphere (Shepard,
1956; Sinopoli, 1991).
Firing Temperature
The oxidization and smudging of pottery is directly related to firing temperature, which also evident in the different colorations found throughout a vessel. In addition to clay minerals (e.g., chlorite, illite, kaolinite, smectite), trace elements in the form of oxides of iron, manganese,
13 magnesium, etc., can affect the color of pottery (Rasmusen et al., 2012). The relative quantities of these elements react with the firing atmosphere and temperature will determine the color of the pottery (Shepard, 1956).
While a reducing atmosphere results in darker colors and smudging and an oxidizing atmosphere creates brighter coloring, the temperature and length of the firing also affects the color of pottery. Similarly, the amount, size, and distribution of oxides, together with characteristics of clay minerals can determine whether pottery will be white, buff, or red when it is fired to a condition of full oxidation (Shepard, 1956). Therefore, conclusions that are drawn solely from color may be misleading without robust mineralogical and chemical analyses
(Tankersley and Meinhart, 1982).
Texture
Texture refers to the ‘feel’ of the clay paste. The constituent materials found within the paste, specifically sand, silt and clay particles affect it. Texture is defined by the composition of the particles and the distribution of grain size (Trziński et al., 2015). A coarse paste will feel gritty but wet fine paste will feel heavy and sticky. The texture of the paste has a direct impact on the way pottery reacts to the formation, drying, firing, and cooling of the vessel (Shepard, 1956).
Archaeologically, the texture of the paste is known as the fabric, which is determined by particle size. The fabric defined by the characteristics of the clay body from which the pottery is made. The resulting fabric of pottery results from the firing temperature, the firing atmosphere, and the inclusions within the clay matrix. The matrix is composed of clay-sized particles (< 0.02 mm) and the inclusions are particles, which are larger. While inclusions can be seen macroscopically, the matrix requires high magnification microscopy to examine. The fabric of
14 pottery is determined by the ceramic raw materials procured and used by ancient potters to manufacture pottery. Both the matrix and inclusions can be affected by the firing temperature and atmosphere (Orton and Hughes, 2013).
Summary
Archaeologists use the physical properties of pottery to classify a vessel and help formulate hypotheses about the cultural development of ceramic technology. While no one physical property can be used to characterize or classify pottery, multiple physical properties have been used to infer levels of technological sophistication and the raw materials procured by ancient potters. One of the goals in the archaeological investigation of ancient pottery is to reconstruct what decisions were made during the ceramic raw material procurement and vessel construction processes that are directly related to the levels of cultural development. Archaeologically, the physical properties of ancient pottery are reflected in the mineralogical and chemical composition of the clay and paste.
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Chapter 3: Archaeological Sites
This thesis examines the raw materials used to manufacture pottery from two contemporary, but geographically distant archeological sites: the main plaza of the Preclassic Maya site of Colha,
Belize (Figure 1) and the Middle Woodland village site known as Twin Mounds in southwestern
Ohio (Figure 1). Samples of pottery were analyzed from these contemporary sites because they were recovered from well-dated and stratified contexts with differing polity levels and ceramic raw material availability. Thus, these sites provide an ideal opportunity to examine whether or not raw materials had limitations on the levels of ceramic technological development. This chapter will provide cultural and temporal information about the archaeological sites from which pottery samples were selected for analysis.
Figure 1. The geographical locations of the Middle Woodland Hopewell Twin Mounds village and
Preclassic Maya Colha sites.
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In Guatemala, Belize, and Mexico, the Preclassic Maya cultural period ranges from ~1000
BCE to ~CE 250 (Webster et al., 2007). The rise of the Maya civilization occurred during the
Preclassic period and is marked with the development of a divine kinship based political structure, and monumental construction (Doyle, 2017). Throughout the Preclassic, pottery developed from rocker stamped gourd-like vessels with simple slips to pots with tetrapod legs and distinctive white and red stripes (Powis et al., 2002; Kosakowsky et al., 2002).
Similarly, in the Ohio and Mississippi River valleys, the Middle Woodland cultural period ranges from ~ 200 BCE to CE 500 (Dalby, 2007; Lane, 2009). During this time, a complex and geographically widespread interaction sphere arose known as the Hopewell cultural tradition. It included burials in log tombs, exotic grave goods, elaborate complexes of mounds and geometric earthworks, and the long-distance trade of raw materials. Hopewell pottery was thin walled with chambered rims and elaborately decorated with highly stylized bird motifs, stamping, incising, and cross etching prior to firing (Carr and Chase, 2005).
Figure 2. The geologic setting of the Preclassic Maya Colha site relative to the source of volcanogenic clays (after Tankersley at al., 2011, 2016).
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Colha
Colha is a Maya archaeological site located near the town of Orange Walk in northern Belize ~50 km north of Belize City (Figure 2). Temporally, the archaeological record of Colha extends from the preceramic Archaic (~3400 BCE) to Postclassic (~CE 1300) cultural periods with cultural peaks during the Late Preclassic (~ 400 BCE-CE 100) and Late Classic (~CE 600-850) (Buttles,
1992). There seems to be evidence at Colha that supports a functional as well as a socio-political arrangement into four quadrants.
The northern quadrant of Colha includes the remains of the largest pastoral and structural arrangements. This area had the most concentrated populations of the prehistoric settlement. Over its long occupation, Colha, did not seem to exceed a population of five thousand people at any one time (Easton, 1980). The west side of Colha features more remote structures than those near the ceremonial center and they are more substantial than those on the western quadrant of the site. The southern portion of Colha contains the area of greatest residential diffusion (Buttles, 1992; Valdez
1987). Hammond (1973) believed that Colha contains important information on the manufacture and specialization of crafts due to the mass amount of lithic scatter and ceramic sherds that were found which was an unusual amount for Lowland Maya. Indeed, there are very few Maya sites that span from Preceramic to Postclassic cultural periods (Valdez, 1987). While a cluster of radiocarbon dates has been obtained for the end of the second millennium BCE at Colha, two age determinations date to the late ninth century BCE and several chronometric age determinations are associated with Preclassic Maya ceramics in the Main Plaza at Colha (Hester 1994). See Table 1.
Colha was initially excavated in 1979 to determine the different types of lithic scatter that were present. Given the success of the first year, a long-term excavation (14 seasons) was planned by Thomas Hester and Harry Shafer from the University of Texas. This investigation began in
18
1979 and was called the “Colha Project” (Hester and Hammond, 1976; Hester et al., 1979). The project focused on lithic workshops in order to obtain a better understanding of craft specialization as well as the development and role of Colha as a center of economic importance. Concurrent with this research, the site was surveyed, mapped, and a variety of structures were excavated (Buttles,
2002).
From these investigations, Richard Adams and Fred Valdez published the first report on
Colha’s ceramic artifacts and their chronologic position (Adams and Valdez, 1979). They reported finding Late Preclassic Maya pottery sherds that were recovered from hearth features located on the exterior of structures and in the context of a midden deposit. In addition to pottery, lithic manufacturing workshops were found to contain ~4,500,000 tools. Monumental architecture was also constructed during the Late Preclassic cultural period. Monumental structures built at this period are consistent with Late Preclassic cultural innovation, craft specialization, and pottery production (Eaton, 1981; Potter, 1981, 1982; Hester and Shafer 1983, 1986, 1994; Shafer 1994;
Buttles, 2002).
Figure 3. The geologic setting of the Twin Mounds site relative to ceramic raw material source areas (after Dalby, 2007). 19
Twin Mounds
Twin Mounds is a multicomponent (Archaic, Middle Woodland, Late Woodland) village site
located in southwestern Hamilton County, Ohio along the extreme margins of an elongated ridge
overlooking the Great Miami-Ohio River confluence area (Figure 3). Geologically, the site is
situated on a high Illinoisan terrace, which contains lacustrine clay deposits that were procured for
the manufacture of pottery. It is underlain by the upper Ordovician age, Cincinnatian Group,
Fairview Formation, a fossiliferous limestone bedrock, which was procured for temper (Potter,
2007; Tankersley and Balyntine, 2010; Tankersley and Haines, 2010).
There are no perennial springs, streams, or permanent sources of water at the site, which
sits ~70 m above with the Ohio and Great Miami rivers. Water was available, however, in the
reservoirs located at the nearby Miami Fort site. A graded causeway more than 900 min length and
some twenty meters in height, more than five kilometers of earthen berms, which vary from few
centimeters to about five meters in height, a broad (about 12 m in width) and deep (about 2.5 m
deep) ditch, and remnants of ancient log and clay dams. The ditches acted as channels, races, and
sluiceways, which drained terraced, bowl-shaped reservoirs (Potter, 2007; Tankersley and
Balyntine, 2010; Tankersley and Haines, 2010).
Starr (1960) first described the location of the Twin Mounds village site. It was initially excavated during the 1965 through 1970 University of Cincinnati Summer archaeological field schools under the direction of Fred Fischer (1965, 1966, 1968, 1969, 1970). The dimensions of the site were recorded as part of an aerial photo mapping survey (Benedict et al., 1968). Fischer (1969,
1970) divided the village site into an eastern and western habitation area. The eastern habitation area included a Middle Woodland village and a large Late Archaic occupation and cemetery and the
20 western habitation area included a Middle and Late Woodland village. Fisher’s excavations exposed household midden deposits, hearths, and storage pits and the remains of a central structure within the western habitation (Fisher, 1970).
In 1971, a controlled test excavation was placed at the center of two burial mounds located
on the southern margin of the eastern habitation area—Twin Mounds, the namesake of the village
site. One of the excavations included a central log tomb containing a fragmentary cremation, a
copper breastplate, and a copper celt, each wrapped in partially mineralized and preserved textile,
along with drilled bear canines, cord marked pottery, Ohio pipestone, and beads made from marine
shell (Lee and Vickery 1972; Lane 2009). Following the salvage excavations in the Twin Mounds,
Lee (1972) continued excavations in the eastern habitation area. The University of Cincinnati
resumed excavations at the Twin Mounds village site as part of their summer archaeological field
school from 2008-2011 (Lane, 2009). A suite of Middle Woodland cultural period radiocarbon
dates has been obtained from the Twin Mounds Village site (Table 1).
Using an assemblage excavated by Fisher, Bennett (1986, 1992, 1996) conducted a detailed
physical analysis and typological study of the Hopewell pottery from Twin Mounds village. The
collection is considered to be largest sample of Middle Woodland pottery from the Lower Miami
region. Her study focused on creating a new typology for Middle Woodland pottery from the area
(Bennett, 1986). Kaltenthaler (1992) conducted a similar typological study using an assemblage of
flaked stone artifacts from the western habitation area.
21
Lab Number 14C Date BP Calendar Year Cultural Period
Colha
TX-8295 2762-2719 813-770 BCE Preclassic
CAMS-8397 2894-2781 944-831 BCE Preclassic
CAMS-8399 3082-2996 1132-1046 BCE Preclassic
CAMS-8398 3085-2995 1135-1045 BCE Preclassic
TX-7371 3213-2956 1263-1006 BCE Preclassic
TX-8106 3264-2876 1314-926 BCE Preclassic
TX-7459 3467-3158 1517-1208 BCE Preclassic
TX-7460 2922-1920 4872-3857 BCE Archaic
TX-8020 3370-3078 5320-5028 BCE Archaic
BETA-64376 3510-3416 5460-5366 BCE Archaic
Twin Mounds Village
BETA-133996 1740-1840 CE 125-381 Middle Woodland
BETA-133998 1690-1890 CE 208-412 Middle Woodland
BETA-145867 1730-1830 CE 128-384 Middle Woodland
BETA-133995 1660-1760 CE 211-433 Middle Woodland
BETA-133997 1600-1700 CE 319-537 Middle Woodland
UGa-4486 910-1400 CE 406-1296 Late Woodland
WIS-1749 1100-1180 CE 850-1030 Late Woodland
Table 1. Radiocarbon dates obtained from the Colha and Twin Mounds Village sites (after Stuiver and Reimer, 1993; Lane, 2009).
22
Summary
The contemporary Preclassic Maya Colha site in Belize and Middle Woodland Hopewell Twin
Mounds Village site in Ohio have been extensively excavated over several decades and have produced a plethora of ceramic artifacts from well-dated stratigraphic contexts. The geologic setting of ceramic raw materials available to ancient potters in these areas is equally well known.
Therefore, pottery sherds from the Colha and Twin Mounds Village sites provide ideal samples for the comparison of ceramic raw materials and the levels of ceramic technological development in these two unique cultural and temporal areas.
23
Chapter 4: Methods and Analyses
Traditionally, archeologists have used “eyeball identification” to determine the ceramic raw material composition of the temper and the paste. Unfortunately, this identification process is highly biased and more often than not, imprecise and inaccurate. A significant problem is that natural inclusions in the paste can easily be mistaken for anthropogenic temper (Tankersley and
Meinhart, 1982). This type of misidentification can skew interpretations about ceramic technological development, production, and use (Tankersley and Haines, 2010). By analyzing the physical and chemical properties of ceramic raw materials using objective and reproducible methods, the resulting data can be quantitatively analyzed and without bias (Tankersley and
Meinhart, 1982). Thus, we can better understand the overall economic behavior of ancient cultures and their ceramic productions.
In this thesis, I use four objective and quantitative analytic techniques to obtain independent proxies of contemporary Preclassic Maya and Middle Woodland Hopewell temper and paste compositions. These techniques include scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffractrometry (XRD), and energy dispersive X-ray fluorescence spectrometry (ED-XRF). These analyses where selected because of their levels of precision. SEM provides an image of raw materials used for paste and temper. XRD is used to determine the mineralogical composition of the paste and temper. EDS and ED-XRF is used to determine the major, minor, and trace element composition of the paste.
24
Pottery Sample
The sample size for this study is comparable to that used in studies by Ford (1995). Because of the time, cost, and destructive nature of mineralogical and geochemical analyses, Ford’s sample size was 11 pot sherds. Dr. Fred Valdez, University of Texas at Austin, provided 31 representative Preclassic Maya pottery sherds from the Colha site in Belize. Radiocarbon and obsidian hydration ages and ceramic typology demonstrate the pottery dates to the Onecimo
Complex, part of the Chicanel Sphere (Valdez, 1987). Dr. Kenneth Barnett Tankersley and the
University of Cincinnati, Court Archaeological Research Facility, provided a comparable sample of 31 Middle Woodland pottery sherds from the Twin Mounds Village site. Radiocarbon ages and ceramic typology show that the pottery dates to the Hopewell Cultural Complex, part of the
Hopewell Interaction Sphere (Lane, 2009). See Table 1.
Physical Properties
Because SEM, EDS, XRD, and XRF are destructive analyses, the physical properties of the pottery sherds were determined prior to laboratory preparation (Table 2) and photographed
(Figures 4 and 5). The Preclassic Maya pottery sherd samples are harder, stronger, less porous, and exhibit brighter colors than the Middle Woodland Hopewell pottery sherds, suggesting they were fired at higher temperatures and in a more oxidized atmosphere (Shepard, 1956).
Sample Preparation
Following physical descriptions and photo-documentation, pottery sherds from the
Hopewell component of the Twin Mounds village site and the Preclassic Maya Colha site were assigned a specimen number between 1 and 31 (see Figures 4 and 5). Sherds were then
25 categorized according to their vessel position (base [Ba], body [B], rim [R], handle [Ha]), positioning of the decoration (interior [INT], exterior [EXT], both [BOTH], none [NONE]), and firing atmosphere (oxidized, oxidized in the center with exterior smudging, smudging in the center, completely smudged, half smudged). For the Hopewell sample, the sherds were tentatively separated into temper type (grit [GRIT] or limestone [LIM]). Subsequently, aliquots of the sherds were cut with a diamond dermal saw. The samples were then ground to a fine mesh with a porcelain mortar and pestle, sifted with a # 70 mesh (212 mm), and placed in labeled glass vials.
Physical Property Preclassic Maya Middle Woodland Hopewell
Hardness (Mohs) 6.0 2.0
Strength (Breakage force 0.6 0.2
exerted by a micrometer)
Porosity (Percent) 88.9 89.5
Color Interior (Munsell) Reddish Yellow Olive Brown 2.5Y 4/3 to Dark 5YR 6/6 to Weak Gray 5YR 4/1 Red 2.5YR 5/2 Color Exterior (Munsell) Pink 7.5YR 8/4 to Black 2.5Y 2.5/1 to Light Reddish Black Brown 7.5YR 6/4 10R 2.5/1 Color Cross-section (Munsell) Very Pale Brown Dark Gray 2.5Y 4/1 to Gray 10YR 8/2 to Pink 5YR 6/1 5YR 8/3 Texture (mm) 0.062 to 0.125 <0.062
Table 2. Physical properties of Preclassic Maya and Middle Woodland Hopewell pottery sherds.
26
Figure 4. Middle Woodland Hopewell pottery sherd sample from the Twin Mounds village site.
Figure 5. Preclassic Maya pottery sherd sample from the Colha site.
27
Two fractions were created for each sherd: a light fraction, the portion of the sample, which passed through the sieve, and a heavy fraction, the portion of the sample, which remained on top of the sieve. Separate mortar and pestles were used for grinding the Hopewell and Preclassic Maya pottery sherd samples. Sparks and burning smells were observed during the cutting of the
Hopewell sherds suggesting that quartz was present, despite the fact it could not be seen with the naked eye nor had it been described in pottery previously examined by Hawkins, Bennett (1986,
1992, 1996) from the site. Samples of temper were isolated and collected from the heavy fraction under a binocular stereoscopic microscope (10-100x). Temper samples were extracted and placed in labeled glass vials.
The light fraction samples were subjected to liquid separation, which used lithium heteropolytugstates to split the sample into heavy and light minerals. Weighted mineral samples were successfully separated from the lithium heteropolytugstates using paper coffee filters and a distilled water spray. The resulting fraction was air-dried leaving a dense amalgamation of light mineral fractions. The contents of the coffee filters were transported to petri dishes, labeled, and examined under a high-magnification light microscope. Photomicrographs were made of exemplary minerals (Figures 6 and 7).
Figure 6. Photomicrographs of quartz, calcite, and clay minerals in sherds from the Colha site.
28
Figure 7. Photomicrographs of quartz, calcite, and clay minerals in sherds from the Twin Mounds village site.
Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometry (EDS)
Scanning electron microscopy and energy dispersive spectrometry was developed by Max Knoll and Ernst Ruska in 1931 to bring higher resolution that light photomicroscopy. Following procedures used by Knappett et al. (2011), exemplary samples of Hopewell and Preclassic Maya temper from the light and heavy fraction were selected for SEM and EDS analyses. Ideally, the smallest representative sample size is best suited for SEM and EDS because the detection range is
~1µm from the sample surface. Aliquots of temper were mounted on standard SEM sample stubs using a conductive double-coated carbon adhesive. The samples were coated with a thin layer of gold using a sputter-coater to make them conductive.
The gold-coated sample stubs were loaded into the vacuum chamber of the SEM with clean
SEM stub forceps. The electron gun directed a stream of electrons through a set of electromagnetic lenses, which directed the electrons towards the sample to prevented obstruction and contamination. The result of this process was an electron imprint, which was converted to a three- dimensional image and digitally saved.
29
Following the digital capture of SEM micrographs, temper samples were analyzed using
EDS. This technique allowed for the chemical analysis of the temper to be observed on the SEM monitor and saved digitally. EDS uses a system of secondary and backscattered electrons that produce X-rays and can be used for the identification and quantification of elements that are present in the samples at detectable concentrations. EDS was used to determine the composition of major and minor elements with concentrations > 0.01 wt% (Tankersley et al., 2018).
Powder X-ray Diffraction Analysis (XRD)
Samples of the light and heavy fraction were prepared for XRD following the methodology described by Tankersley and Ballantyne (2010) and Tankersley et al. (2011). Aliquots of Hopewell and Preclassic Maya pottery sherds were mixed with deionized water to make slurry in a 100 ml beaker. The samples were then dispersed using a high-speed stirrer and gravity settling to obtain a fraction of <2 mm. A 5 ml pipette was used to transfer the clay sample from the top of the slurry to a glass slide and then allowed to air-dry.
An XRD pattern was obtained for prepared samples by initially scanning them from 2o to
32o 2θ at 0.5 increments and then broadened to 72o 2θ on a Siemens D-500 X-ray diffractometer using a Cu-Ka radiation source. The intensity threshold was set at 1.6. Mineral composition was identified on the basis of peak position and intensity (Chen, 1977).
Energy Dispersive X-Ray Fluorescent Spectrometry (ED-XRF)
The minor and trace element mass fractions of Hopewell and Preclassic Maya sherd samples determined by ED-XRF following the methods described by Tankersley et al. (2018). Each powdered sample was pressed into a pellet following procedures described by Ingham and
30
Starbuck (1995) and Hunt et al. (2014). Approximately 10 g of powdered each sherd sample was mixed with 2 ml of Elvacite acrylic resin dissolved in a mixture of 1 l of acetone and 200 g of
Elvacite powder. The samples were then carefully mixed in a mortar and pestle until the sample was homogenized (Tankersley et al., 2018). The resulting aliquot was placed into a 40 mm aluminum cup and placed in a pellet-press die and compressed using a hydraulic press between
1.59–1.72 Å~ 10−8 Pa for three minutes (Tankersley et al., 2018). A controlled pressure release over a period between 30 and 60 s provided a consistent analytical surface (Hunt et al., 2014).
The powder pressed samples were then analyzed for minor and trace elements on a
ThermoScientific ARL Quant'X ED-XRF analyzer. Each sample was excited using a Rh tube with a Be end window. The dispersed X-rays were collected using a Si drift detector following the methods described by Shackley (2011) and Hunt et al. (2014). The X-ray flux and current setting was automatically adjusted to reduce the effects of Compton peak scatter.
Summary
The physical properties of the samples (62 pottery sherds, 31 aliquots from the Preclassic Maya
Colha site in Belize and 31 aliquots from the Hopewell Twin Mounds Village site in Ohio) were described using semi-quantitative characteristics. The mineralogical and chemical composition of the ceramic raw materials was determined using SEM, EDS, XRD, and ED-XRF analyses.
31
Chapter 5: Results
SEM, EDS, XRD, and XRF analyses of 62 pottery sherds provide the mineralogical and chemical composition of the ceramic raw materials used in the production of Preclassic Maya and Hopewell pottery. These techniques provide crucial data on the physical, mineralogical, and chemical properties of the pottery.
Scanning Electron Microscopy (SEM)
Scanning electron microscopy was used to identify the raw material composition of temper in
Hopewell pottery sherds excavated from the Twin Mounds Village site and Preclassic Maya pottery sherds excavated from the Colha site (Figures 8 and 9).
Figure 8. SEM micrographs of temper raw materials from Hopewell pottery sherds from the Twin
Mounds Village site.
32
SEM analyses demonstrate that the Hopewell pottery sherds from the Twin Mounds village site contain both carbonate (e.g., calcite) and silicate minerals (e.g., biotite), which demonstrates that sedimentary (i.e., limestone), igneous (i.e., granite), and metamorphic rocks (i.e., schist) were used for temper (Figure 8). All of these rocks and minerals were locally available. Upper Ordovician limestone bedrock outcrops at the site and granite and schist occur in the late Pleistocene glacial gravels exposed along the Great Miami River (Dalby, 2007). Similarly, SEM analyses demonstrate that Preclassic Maya pottery sherds from the Colha site also contain both carbonate (e.g., calcite) and silicate minerals (e.g., quartz), which were used for temper (Figure 9). These minerals were locally available in the alluvium, which contains angular, coarse-grained deposits of quartz with minor amounts of calcite (Tankersley et al., 2011, 2016). SEM analysis also revealed smectite and kaolinite in the clay paste for the Colha samples (Figure 9).
Figure 9. SEM micrographs of temper and paste raw materials from Preclassic Maya pottery sherds from the Colha site.
33
Energy Dispersive Spectrometry (EDS)
EDS analysis was conducted to identify the major elemental composition of Hopewell pottery sherds from the Twin Mounds village site and the Preclassic Colha site (Tables 3 and 4). Hopewell pottery sherds from Twin Mounds contained the elements Al, C, Ca, Fe, Mg, Na, O, P, Si, and Ti and are likely associated with the minerals and rocks biotite, calcite/limestone, chlorite, illite, kaolinite, quartz, and smectite. The biotite, calcite/limestone, and quartz occur in the pottery sherds as temper and the clay minerals chlorite, illite, kaolinite, and smectite occur in the pottery as paste.
The titanium and phosphorus are likely associated with one or more of the clay minerals (Table 3).
Table 3. EDS analysis of Hopewell pottery sherds from the Twin Mounds village site.
Pottery sherds from the Colha site contained the elements Al, C, Ca, Fe, Mn, O, Si, and Ti and are likely associated with the mineral’s calcite, kaolinite, quartz, and smectite. The calcite and
34 quartz occur in the pottery sherds as temper and the clay minerals kaolinite and smectite occur in the pottery as paste. The manganese and titanium are likely associated with one or more of the clay minerals (Table 4).
Table 4. EDS analysis of Preclassic Maya pottery sherds from the Colha site.
X-ray Diffractometry Analysis (XRD)
XRD analysis was conducted to identify the mineralogical composition of ceramic raw materials from the Twin Mounds village and the Preclassic Colha site (Figures 10, 11, 12, and 13). The minerals calcite and quartz were found in the Hopewell pottery sherds as temper (Figure 12). Clay from Illinoisan lacustrine deposits and Upper Ordovician Fairview Formation shale from the immediate vicinity of the Twin Mounds village site and were found to contain the minerals chlorite, illite, kaolinite, smectite (Figure 11). These clay minerals may have been procured for paste from either lacustrine deposits or shale, as the underlying lacustrine deposits contain a high quantity of smectite and would have produced a higher quality paste (Figure 11).
35
Figure 10. XRD analysis of Hopewell pottery sherds from the Twin Mounds village site.
Figure 11. XRD analysis of ceramic raw materials from the vicinity of the Twin Mounds village site (after Tankersley and Balyntine, 2010).
36
Figure 12. Mineralogical composition of clay minerals at the Twin Mounds Village site.
Similarly, the minerals calcite and quartz were found in the Preclassic Maya pottery sherds as temper (Figure 14). Clay from local ponded sediments in the vicinity of the Colha site were found to contain the minerals kaolinite and smectite (Figure 13). These clay minerals produced a very high quality paste (Figure 13).
Figure 13. XRD analysis of ceramic raw materials from the vicinity of the Colha site (after
Tankersley et al., 2011, 2016).
37
Figure 14. XRD analysis of Preclassic Maya pottery sherds from the vicinity of the Colha site.
Energy Dispersive X-ray Fluorescent Spectrometry (ED-XRF)
ED-XRF analysis of Hopewell pottery sherds from the Twin Mounds village site and Preclassic sherds from the Colha Maya site was conducted to measure the quantity of the minor elements Al,
Ca, Fe, K, Mg, Mn, P, Si, and Ti (Table 5) and the trace elements As, Ba, Co, Cr, Cu, Nb, Pb, Rb,
Sr, Th, U, V, Y, Zn, and Zr (Table 6). A t-test was used to determine whether there was a significant difference between the quantity minor elements in the Hopewell and Preclassic Maya pottery sherds.
T-value Calculation Elements (Mg, Al, Si, P, K, Ca, Ti, Mn, Fe)
2 2 2 s p = ((df1/(df1 + df2)) * s 1) + ((df2/(df2 + df2)) * s 2) = ((8/16) * 353.18) + ((8/16) * 306.27)
= 329.72
2 2 s M1 = s p/N1 = 329.72/9 = 36.64
2 2 s M2 = s p/N2 = 329.72/9 = 36.64
2 2 t = (M1 - M2)/√(s M1 + s M2) = -0.03/√73.27 = 0
38
The t-value is -0.00364. The p-value is .997145. The result is not significant at p < .10. The insignificance of the differences of the minor elements is likely because they are associated with the minerals calcite, kaolinite, quartz, and smectite, which occur in both the Hopewell and
Preclassic Maya pottery sherds.
Another t-test was used to determine whether there was a significant difference between the quantity of trace elements in the Hopewell and Preclassic Maya pottery sherds.
T-value Calculation Trace Elements (As, Ba, Co, Cr, Cu, Nb, Pb, Rb, Sr, Th, U, V, Y, Zn,
Zr)
T-value Calculation
2 2 2 s p = ((df1/(df1 + df2)) * s 1) + ((df2/(df2 + df2)) * s 2) = ((15/30) * 70478.2) + ((15/30) *
6373.67) = 38425.93
2 2 s M1 = s p/N1 = 38425.93/16 = 2401.62
2 2 s M2 = s p/N2 = 38425.93/16 = 2401.62
2 2 t = (M1 - M2)/√(s M1 + s M2) = 91.5/√4803.24 = 1.32
The t-value is 1.32024. The p-value is .098369. The result is significant at p < .10. The significance of the differences of the trace elements is likely because they are associated with the clay minerals chlorite and illite, which only occur in the Hopewell pottery sherds. These minerals are absent in the Preclassic Maya pottery and were unavailable in the vicinity of the Colha site.
39
Table 5. XRF analysis of major elements in Hopewell pottery sherds from Twin Mounds village
site and Preclassic pottery sherds from the Colha site.
Table 6. XRF analysis of pottery sherds from Twin Mounds village and Colha sites.
40
Summary
Significant mineralogical and chemical differences were found in the ceramic raw materials used to manufacture Preclassic pottery at the Colha site in Belize and Hopewell pottery at the Twin Mounds
Village site. Indeed, the paste of the Preclassic Colha pottery is dominated by smectite and kaolinite and the paste of the Hopewell Twin Mounds Village pottery is dominated by chlorite and illite.
Additionally, levels of MgO, P2O5, K2O, CaO, Ti, and Fe2O3 in the major elements and the Ba, Ni, Rb,
Sr, V, Y, and Zn in the raw materials were what made the Colha and Hopewell pottery completely different from one another. These mineralogical and chemical differences correlate with physical properties such as strength and porosity. Smectite and kaolinite paste used to manufacture the
Preclassic pottery at the Colha site resulted in strong vessels with low porosity. Chlorite and illite paste used to manufacture the Hopewell pottery at the Twin Mounds Village site resulted in brittle pottery with high porosity.
41
Chapter 6: Discussion and Conclusion
This thesis used a suite of mutually exclusive proxies including SEM, EDS, XRF, and ED-XRF to determine whether or not the Preclassic Maya potters at the Colha site in Belize were advantaged in terms of ceramic raw materials when compared to the contemporary Hopewell potters at the
Twin Mounds Village site in Ohio. While both potters at both sites used the minerals calcite and quartz for temper and the clay minerals kaolinite and smectite for paste, there were significant differences. For example, while the Hopewell Twin Mounds Village pottery contains some kaolinite and smectite, the paste is predominately composed of chlorite and illite. Preclassic Maya pottery at the Colha site, on the other hand, lacks chlorite and illite and is dominated by kaolinite and smectite.
Ceramic pastes made from the clay minerals chlorite and illite has minimal shrinkage during the drying, firing, and cooling processes of pottery production. Consequently, Hopewell pottery at the Twin Mounds Village site made from these clay minerals resulted in highly porous earthenware. Ceramic pastes made from the clay minerals kaolinite and smectite, on the other hand, have a high degree of shrinkage during the drying, firing, and cooling processes of pottery production. Thus, Preclassic Maya pottery at the Colha site made from these clay minerals resulted in earthenware with a low porosity. Pottery with lower porosity is more tenacious, has the ability to hold water for longer periods, and has higher refractory properties, which allows it to withstand repeated heating during cooking. Hopewell pottery from the Twin Mounds Village site, in contract, was more brittle, would hold water only for short periods of time, and eventually broke from repeated heating.
42
The availability of ceramic raw materials may explain, in part, why Preclassic Maya pottery from the Colha site was technologically more sophisticated than contemporary Hopewell earthenware from the Twin Mounds Village site. While this study focused on two sites, one from the Maya Lowland and one from the Ohio valley, it is quite likely that these sites are representative of these regions. The Preclassic Maya lived in an area, which experienced periodic ash falls from catastrophic volcanic events. The ash quickly decomposed into high quality ceramic raw materials—kaolinite and smectite clay minerals (Tankersley et al., 2011, 2016). The Hopewell lived in the Ohio River valley, which did not have access to high quality volcanogenic clays
(Tankersley and Meinhart, 1982; Dalby, 2007, Tankersley and Haines, 2010). This broad cross- regional comparison, can and should be investigated using the techniques outlined in this thesis.
In terms of cultural evolution, technology is considered a driving force behind cultural evolution, which provides humans with a means to survive and ultimately adapt. In this regard, ceramic technology can be viewed as an important facet of cultural survival and adaptation in complex agricultural based polities. Because the availability and quality of raw materials (i.e., physical properties and chemical composition) limited the rate and ultimately the level of ceramic technological development, some cultures were more advantaged than others. Higher quality ceramic raw materials allowed for greater technological developments and innovations, which went far beyond basic subsistence function.
This evolutionary view of the role of ceramic raw materials rate and the level of technological development of pottery complex polities is unique. While this study focused on the
Western Hemisphere, the techniques can be applied to any technological ceramic complex or time period in the world. It is quite likely that other cultures with highly advanced ceramic technological development were similarly advantaged because of the availability of high-quality
43 clay mineral resources. It is hoped that future archaeological investigations will use the techniques presented in this thesis to investigate the mineralogical and chemical composition of pottery from other time periods and culture areas.
44
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