Production and Distribution of Plumbate Pottery: Evidence from a Provenance Study of the Paste and Slip Clay Used in a Famous Mesoamerican Tradeware

Results 1: Raw Material Sources for Plumbate Pastes

The Plumbate sherds analyzed by INAA since 1993 at MURR showed the same basic chemical patterning reported previously by Neff (1984; Neff and Bishop 1988). That is, the vast majority of analyzed specimens fall into one of two compositional groups, designated San Juan and Tohil in recognition of consistent typological differences. Sherds of San Juan composition are exclusively "background tradition" bowls, cylinders, large jars ("Robles jars"), and large everted rim vessels of various shapes. The Tohil group not only includes background tradition vessels, but also lamp chimneys, Tohil jars, effigies, figurines, and other forms typical of the fancy Tohil style (see Neff 1984 for descriptions). Chromium and iron concentrations (Figure 11, below) easily discriminate the compositional groups, as do many other bivariate plots of the INAA data. Figure 11 also shows iron and chromium concentrations determined by INAA in the raw clays from the Plumbate production region. Although the clays are generally much more variable than the pottery, a number of clay samples fall within the ranges of variation of both reference groups on these axes. More detailed identification of where the two groups might originate within the Plumbate production region must be based on a similarity assessments obtained from a broader range of elemental concentrations data.

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With well-defined reference groups such as those shown in Figure 11, provenance determination resolves to a search for locations where there are raw clays that fall within the range of chemical variation of the two groups (Neff 1998, 2001; Neff and Bove 1999). Whether a clay falls within the range of variation of a group can be measured by its multivariate proximity to the group centroid (the Mahalanobis distance), which can be expressed as a probability of group membership. These point probabilities can be used to estimate a probability surface for the sampled region; peaks or plateaus on the surface are the areas most likely to have clays that fall within the range of chemical variation of the group.

Probabilities for the clays can be generated using different subsets of the samples and different subsets of elements. Based on the MURR data and using elements that best discriminate the two groups, the San Juan source is placed on the east side of the border, near the mouth of the Río Naranjo (Figure 12), and the Tohil source is placed on the west side of the international border, along the Río Cahuacan (Figure 13). Probability surfaces based on much larger reference groups consisting of MURR data together with the BNL data and using different subsets of the elements are configured a little differently, but still place the San Juan and Tohil source zones in the same areas.

Comparison of the raw clays collected in the Plumbate source region with the Plumbate reference groups thus leads to a highly specific understanding of the provenance of the two Plumbate pastes. The San Juan and Tohil source zones do not overlap, and both are quite localized on the lower coastal plain near the present México-Guatemala border. Most of the sites in the region where large quantities of Plumbate are found, such as Santa Romelia, El Sitio, and Izapa, appear to lie outside of either of the two zones where Plumbate was produced.

This new evidence finally puts to rest any doubt about where the fancy Tohil plumbate vessels found in tombs and offerings all over Mesoamerica were produced. The Tohil Plumbate compositional group, which includes vessels in this fancy style, is now clearly linked with raw materials sampled along the lower reaches of the Río Cahuacan in southern Chiapas, México. Observations made during our raw materials survey indicate that Plumbate sherd densities are extremely high in the banana fields that dominate the modern landscape on this part of the coastal plain. Future work will be aimed at locating and excavating firing areas and other production facilities within this region.

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