10. Trace-element Analysis on Pottery from Oaxaca

10. Trace-element Analysis on Pottery from Oaxaca

10. Trace-element Analysis on Pottery from Oaxaca

10 examples of pottery - Authors: R. Jason Sherman (University of Michigan, Ann Arbor), Leah Minc (Oregon State University Radiation Center), Christina M. Elson, Charles S. Spencer, Elsa M. Redmond (American Museum of Natural History)

In this article we will discuss preliminary data from the results of trace-element analyses on gris and crema paste pottery from three sites in the Ocotlán-Zimatlán subregion of the Oaxaca Valley, Mexico. To begin, we provide an outline of work carried out at these sites (for more detailed information on work at these sites, see the publications listed in "For Further Reading" at the end of the article).

El Palenque

Area I Palace

From 1993 to 2000, Charles Spencer and Elsa Redmond directed a project including site mapping, the systematic collection of surface materials, and excavation at the site of El Palenque located near the modern town of San Martín Tilcajete. Excavations uncovered a palace, two temples, and a residence. All the excavated buildings are situated around the site's Main Plaza. Radiocarbon samples from the palace provided conventional dates between 350 BC + 80 and 20 BC + 60. Based on these dates and the analysis of associated materials, it can be stated with confidence that the palace was in use during Monte Albán Late I (300-100 BC). At the end of this period, the palace burned and the site of El Palenque was abandoned.

Cerro Tilcajete

Period II Plaza

Some of the El Palenque's population moved to Cerro Tilcajete, which is located on the top of a ridge, some 300 m above the level of the valley floor. In 1994, Charles Spencer and Elsa Redmond mapped and surface collected Cerro Tilcajete. The material from the surface collections indicates that the site was occupied during Monte Albán II (100 BC - 200 AD) and Monte Albán IIIB-IV (AD 500-1000). Between 1999-2003, Christina Elson directed the excavation of a palace, a two-room temple, and an elite residence, all situated around Cerro Tilcajete's small Period II plaza. In addition, a low-status house located on a terrace 260 m away from the plaza was excavated. A radiocarbon date from the platform sustaining the palace was 130 AD + 60. Based on this date and on the associated ceramic material, it can be said with confidence site was first occupied in the Monte Albán II Period when it functioned as a secondary center for the Ocotlán-Zimatlán region.

Yaasuchi

In 2001 and 2002, Jason Sherman investigated the site of Yaasuchi located in the district of Zimatlán between the towns of El Carmen and La Raya de Zimatlán. The site was mapped and systematically surface collected. In addition, Sherman excavated a residence, a temple, and a civic-ceremonial building. The ceramic data indicate that Yaasuchi was occupied in Monte Albán Late I, Monte Albán II, and Monte Albán IIIB-IV. In Monte Albán II, Yaasuchi was a third-order site in the regional settlement hierarchy.

The Trace-element Analysis Project

In 2002, with the support of the American Museum of Natural History and the University of Michigan, Leah Minc and Jason Sherman analyzed 168 ceramic samples using Trace-element Analysis. The samples were analyzed in the Ford Research Reactor at the University of Michigan. In general, the analysis was designed to evaluate the relationship between ceramics from the Ocotlán-Zimatlán subregion and ceramics from Monte Albán.

Our thanks go to Dr. Marcus Winter and Lic. Cira Martínez-López who provided the 23 samples from Monte Albán and to the Archeology Commission of The National Institute of Anthropology and History, Mexico and Lic. Joaquín García Bárcena for granting us permission to take the samples to the US.

Four common
paste types

A Basic Definition of the Four Most Common Paste Types
In La Cerámica de Monte Albán (1967) Alfonso Caso and his colleagues laid out the ceramic sequence for Monte Albán after 500 BC. They identified four common paste types:
crema (C) and café (K) ceramics, which are made from piedmont clays and
gris (G) and amarillo (A) ceramics, which are made of finer alluvial clays.

Many (but not all) amarillo types are actually gris wares fired in an oxidized environment. Clay sources are found throughout the Oaxaca Valley. In the same volume, Anna Shepard presented the results of a petrographic analysis of Monte Albán ceramics. She recognized that while gris, café, and amarillo pastes are quite variable in terms of their composition (paste plus temper), crema ceramics have a much more uniform consistency. As stated before, here we are going to focus on information related to the production and distribution of gris and crema wares. In terms of these types, Shepard stated that gris ceramics contain primarily sand as temper, but sometimes they contain diorite, fine diorite or a mix of sand and diorite. Crema ceramics contain primarily diorite as temper.

C.6, C.7, C.12
G.12, G.17, G.21


Anna Shepard was the first researcher to suggest that the clay and temper used to produce crema ceramics came from mines close to Sta. María Atzompa, a town located at the base of Monte Albán. Thus, Caso and his colleagues suggested that these ceramics were Monte Albán wares. Chemically, the minerals that make up diorite include plagioclase feldspar, amphibole hornblende, and others like quartz, biotite, mica, and olivine. The preponderance of feldspars and amphibole leaves a chemical signature noticeable for its high values of sodium, calcium, and associated elements like strontium. The majority of the samples submitted for analysis (less 10 Monte Alban IIIb-IV sherds from Yaasuchi) are good Monte Albán I and II diagnostics and are well described in La Cerámica de Monte Albán. Among these are crema types like C.2, C.4, C.6, C.7, C.11, C.12, C.20 and gris types like G.15, G.17, G.12, G.21.

Table 1. Sites and the number of ceramic samples of each paste type submitted for trace-element analysis.
Paste	El Palenque	Cerro Tilcajete	Yaasuchi	Monte Albán	Total: paste
Crema	6	13	13	7	39
Gris	11	29	34	10	84
Café	4	15	10	4	33
Amarillo	0	3	4	2	9
Other	0	2	1	0	3
Total: site	21	62	62	23	168

During the analysis of the ceramics from Cerro Tilcajete and Yaasuchi, Elson and Sherman identified a ceramic type Caso and his colleagues called the G.29. Spencer and Redmond did not find this type in their collections from El Palenque. In La Cerámica de Monte Albán (p. 45), Caso and his colleagues state that the G.29 dates to Monte Albán II (100 BC-AD 200) and they provided the following description:

    "It is without doubt an intrusive type, its paste is different than that of the common types of Monte Albán. It appears, however, similar to pastes with a sandy quartz temper, but different from them in that it has opaline inclusions in the form of small spicules. It is a sandy gray clay, the vessels are medium thick to thin walled, and they have a green-café wash that is polished on both sides. Over the wash there are red paint splotches and the rim almost always has a polished red stripe. Sometimes the entire vessel has sloppily applied red paint, which gives it the appearance of a C.7. There is a variant with incised lines near the border and the only forms we have are vases and maybe comals."
    (translation by the authors)

G.29 from Cerro Tilcajete

G.29 from Yaasuchi

There are several points that can be made about G.29 ceramics from Cerro Tilcajete and Yaasuchi:

    Examples of this type have a surface color that ranges from light coffee color to orange to almost black.
    Most examples have red paint on one or both sides.
    The most diagnostic aspect of the ceramic is that it is a dark, dense paste that has a sandy quartz temper and opaline inclusions.
    As Caso et al. suggested, a good description of this type is that it is a type intended to imitate crema ceramics. In particular, many are imitations of cremas with red paint called C.7 and C.11.
    At Cerro Tilcajete and Yaasuchi, the majority of the vessels are bowls. Elson and Sherman have proposed that while the G.29 is an intrusive type to Monte Albán, it clearly is common in Period II contexts in the Ocotlán-Zimatlán subregion and may have been produced there.

Gris, Crema and G.29 Ceramics in Excavated Samples
Before proceeding to a discussion of the results of trace-element analyses on G.29, crema, and gris ceramics, it is relevant to provide more specific data about the relationship between these three types in our excavated samples.

G.12, G.17

At the site of El Palenque in Monte Albán Late I (300-100 BC), gris types like the G.12 and the G.17 are abundant in excavations. Visually, gris ceramics vary in their color and composition, so there could have been several loci for their production. In comparison, during the same period the crema wares thought to come from Monte Albán are very scarce in excavated contexts. For example, excavations in the Area I palace uncovered very few crema wares (C.6, C.7, C.13 and C.20) that are so common at Monte Albán during the same time period. Spencer and Redmond have suggested that the lack of crema wares at El Palenque is one line of evidence that, among others, suggests that El Palenque and Monte Albán had a hostile relationship in Monte Albán Late I.

C.7, C.11

During the Monte Albán II Period, Cerro Tilcajete became the subregion's secondary center. At Cerro Tilcajete, cremas are quite abundant in excavated elite contexts. For example, in the Area A palace, cremas constitute 30% of all diagnostics while in the low status house cremas made up 12% of the diagnostics. The people of Cerro Tilcajete clearly had regular access to crema pottery, suggesting a much closer relationship between this site and Monte Albán. Excavations at Yaasuchi produced gris types and crema types. One interesting result from excavations at Yaasuchi and Cerro Tilcajete was a comparison of the relative abundance of G.29 ceramics at the two sites, which is presented in table 2.

Table 2. A comparison of the relative abundance of G.29 ceramics at Yaasuchi and Cerro Tilcajete.
	C.7/C.11	G.29
Cerro Tilcajete
Elite context	11.7%	0.6%
Low status context	6.2%	6.8%
Yaasuchi (entire site)	3.0%	4.5%

A comparison of the frequency of this type at the two sites allowed Elson and Sherman to hypothesize that the G.29

    was used more commonly by people with a lower social status than crema ceramics
    occurs more frequently at smaller sites (those positioned lower in the subregional hierarchy)
    was produced in the Ocotlán-Zimatlán subregion

Preliminary Results From Using Trace-element Analyses to Test Hypotheses About Gris, Crema, and G.29 Ceramics
The trace-element analysis results have helped test hypotheses regarding the production and distribution of gris, crema, and G.29 ceramics. These include the suggestions that:

    In Monte Albán Late I and II, crema ceramics are a generally homogenous ceramic type produced in the vicinity of Monte Albán and transported to other sites in the valley.
    In Monte Albán Late I, gris ceramics like G.12 bowls and G.17 plates, which can have standardized designs and forms, may have been produced in several places in the valley.
    In Monte Albán II, G.29 ceramics probably are made from clays occurring in the Ocotlán-Zimatlán subregion.

In table 3 and the diagram showing the separation of major paste groups, we show that trace-element analyses identified three principal composition groups which we have called PC 1-3. The probability that a sample pertained to one of the three groups was determined using the Mahalanobis D2 statistic. PC group 1 has no subgroups. PC group 2 has two subgroups. PC groups 3 has three subgroups.

Table 3. Description of three principal compositions groups identified by trace-element analysis.
Group	Description
PC 1	These ceramics characterized, as expected by elevated concentrations of sodium, have diorite temper: 90% (36 of 40) of the types identified in the field as cremas (C) belong to this group. The group includes all crema samples from El Palenque.
PC 2	Sand-tempered ceramics characterized by significantly higher concentrations of the rare earth elements. Statistically, this group has two strongly marked divisions.
	Subgroup	Description
	A group high in iron (Fe) and sodium (Na)	Includes both gris (G) and café (K) sherds.
	A group low in iron and sodium	This is the G.29 ceramic type: 90% (17 of 19) of the samples identified in the field as G.29 belong to this group as do two sherds from Monte Albán identified as K3.
PC 3	Sand-tempered ceramics with distinctively high concentrations of rubidium, cesium, and thorium. The three subgroups are statistically significant, but the divisions are less strongly marked than those of the PC 2 subgroups.
	Subgroup	Description
	A group high in cesium (Cs)	Several types including red painted amarillo (A.9) sherds from Cerro Tilcajete, Monte Albán, and Yaasuchi and gris sherds (excluding all G.29) from the same three sites.
	A group high in Antimony (Sb)	A mix of several gris and café types.
	A group high in thorium (Th) and rubidium (Rb)	Only gris types: 8 of the 10 samples are from El Palenque and five of these eight are the bottoms of G.12 bowls.

Diagram. Separation of major paste groups.

Discussion
In general, trace-element analyses have been useful tools to begin probing ideas about the production and distribution of pottery in the Monte Albán I and Monte Albán II Periods. Thus far, regarding crema ceramics, we feel that trace-element analyses support the ideas that:

    Crema ceramics are very homogenous in their terms of their chemical composition.
    In general, it is possible to correctly identify crema ceramics in the field.
    The vast majority of crema ceramics were produced in the vicinity of Monte Albán.

Based on the results of trace-element analyses and our site-specific excavation data we suggest that:

    In Period Late I (300-100 BC) scarcity of crema ceramics at El Palenque supports the interpretation that El Palenque and Monte Albán had a relationship which impeded economic exchange between the two sites. Much of the Ocotlán-Zimatlán subregion may not have been integrated into the Monte Albán state.
    In Period II (100 BC-AD 200), the subregional center shifted to Cerro Tilcajete and local elites had abundant access to crema ceramics. During this period, the site functioned as a secondary center and the Ocotlán-Zimatlán subregion was well-integrated into the Monte Albán state.

Thus far, regarding gris ceramics, we feel that trace-element analyses support the ideas that:

    Gris ceramics are less homogenous in terms of their chemical composition.
    Some gris ceramics, and very probably G.29 ceramics, likely were produced in the Ocotlán-Zimatlán subregion.

Based on trace-element analyses and our site-specific excavation data we suggest that:

    In Period Late I, some decorated gris ceramics used at El Palenque like G.12 bowls or G.17 plates may have been produced in the Ocotlán-Zimatlán subregion. Gris pottery production may not have been centralized.
    In Period II, gris ceramics continue to vary in terms of their composition. In addition, other locally-produced ceramic types appear. The most significant is called the G.29. This type likely was produced in the Ocotlán-Zimatlán subregion to imitate crema ceramics. The G.29 was consumed with greater frequency by lower status members of society and populations at smaller centers (tier 3-5 sites) in the subregional hierarchy.

In conclusion, trace-element analyses have shown to be useful for contributing new data on ceramic production and exchange during the Monte Albán Late I and Monte Albán II time periods. However, we caution that these results and our interpretations of the data should be regarded as preliminary. Firmer conclusions must rest on the analysis of many more vessels as well as the analysis of clay samples from throughout the Oaxaca Valley.

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