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Harriet F. Beaubien (1) and Emily Kaplan (2)
An unusual material - identified as a composite formed from several layers of woven textile in a clay matrix - has recently been found at two archaeological sites in the Petexbatún region of Guatemala. Several reconstructible objects appear to be ceremonial gear, including possible mask and headdress elements.
Aguateca. Fragments were part of burned floor assemblages from a probable royal palace located in the site's elite center and dating to the Late Classic period around AD 800. The majority were found during 1998 excavations under the direction of Takeshi Inomata (University of Arizona), Daniela Triadan (SCMRE) and Erick Ponciano (Universidad Del Valle, Guatemala).
Las Pacayas (Cueva de los Quetzales). Fragments came from unstratified ceremonial deposits, dating from Late Preclassic to Late Classic (before AD 250 to 900), in a cave underlying the site's center. They were found during 1993 excavations under the direction of James E. Brady (California State University, Los Angeles) and Irma Rodas (Universidad San Carlos).
Definition of a composite
A composite is defined as a material created by the synthetic assembly of two or more components: a filler or reinforcing agent, and a matrix or binder in which the filler is embedded. These may form a single layer (lamina) or a laminate, a stack of laminae in various orientations usually bound together with the same matrix as is used in the individual laminae.
Analysis of components
Fiber. Based on some directly preserved fibers in Las Pacayas fragments, and otherwise examination of impressions in the clay matrix, all threads are Z-twist most commonly with a diameter of ~0.5mm. FTIR analysis of surviving fiber samples indicates a cellulosic (plant) fiber.
Weave structures. Aguateca textiles are primarily variations of plain weave and one possible twill weave, studied easily with polyvinyl siloxane casts of impressions in the clay matrix. Common ones include two balanced types (one at ~12x13 threads/cm and a more open one at ~6x8 threads/cm) and a warp/weft-faced type (at ~6x15 threads/cm). Las Pacayas textiles, from impressions in the clay matrix, are plain weave with a paired warp/weft at ~8x24 threads/cm.
The matrix produces EDS spectra of elements comparable to clays, and SEM images show a glassy structure comparable to fired clay.
The lamination process involved layering textile pieces dipped in clay slip, to build up a thickness ranging from several millimeters to approximately 1cm. This process required the use of a form (or mold), which, from finely striated impressions remaining on interior surfaces of some Aguateca fragments, was possibly made of wood. Aguateca fragments also indicate that the layering process progressed from interior to exterior, with decorative details worked into the outermost layers. These included folds, incised grooves and red coloration (using an iron-based pigmented slip).
Once dried, the objects were likely hardened by heat as a stage of manufacture, although later heat exposure (at deposition) is known to have occurred particularly at Aguateca. All fragments were resilient when immersed in water. When a Las Pacayas sample was heated up to 700° and then 850°C, color differences in the matrix disappeared to produce a uniform terra-cotta color and even at these temperatures, remnant fibers were not visibly changed. Laboratory samples were made to investigate aspects of fabrication, including heating at 100°C increments from 350° to over 1000°C to evaluate the effects on components and overall structure.
A textile-clay composite would have been a highly suitable material for ceremonial gear: easily shaped into elaborate forms, producing rigid yet lightweight objects that could be used more than once and in damp conditions. The skillfulness of these artifacts gives good indication that this technology was an established one despite the absence of other excavated examples. By ethnographic analogy and similarity from a materials science perspective, the modern cartonería tradition may represent a survival of this ancient craft technology.
Has anyone else seen a composite material like this? Please contact us.
Las Pacayas (Cueva de los Quetzales, Guatemala)
Brady, James E. and Irma Rodas. Undated. Maya ritural cave deposits: recent insights from the Cueva de los Quetzales. Institute of Maya Studies Journal I #1: 17-25.
Kaplan, Emily. 1994. Technical report: fragments from Cueva de los Quetzales, Petexbatún Regional Archaeological Project. CAL #5449, Smithsonian Center for Materials Research and Education (unpublished report, 1994).
Inomata, Takeshi, Daniela Triadan, Erick Ponciano, Richard E. Terry, Harriet F. Beaubien, Estela Pinto y Shannon Coyston. 1998. Residencias de la familia real y de la elite en Aguateca, Guatemala. Mayab 11: 23-39.
Beaubien, Harriet F., Stephanie E. Hornbeck and Elizabeth C. Robertson. 1998. Artifacts conservation during the 1998 season, Aguateca Archaeological Project. SCMRE #5668, Smithsonian Center for Materials Research and Education (unpublished report, 1998).
Beaubien, Harriet F. and Joanne M. Boyer. 1999. Artifacts conservation during the 1999 season, Aguateca Archaeological Project. SCMRE #5668, Smithsonian Center for Materials Research and Education (unpublished report, 7 September 1999).
Shah, Monica. Technical investigation of textile/clay composite samples from Aguateca. SCMRE #5695, Smithsonian Center for Materials Research and Education (ongoing research, 1999-2000).
H.F. Beaubien, MCI, 5/00
Summary of Poster, 32nd International Symposium on Archaeometry, 15-19 May 2000, Mexico City
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1. Smithsonian Center for Materials Research and Education (SCMRE), Museum Support Center, 4210 Silver Hill Road, Suitland, MD 20746-2863 USA, Tel: 301-238-3700x 154; Fax: 301-238-3709; E-mail: firstname.lastname@example.org
2. Smithsonian Institution, National Museum of the American Indian Cultural Resources Center, 4220 Silver Hill Road, Suitland, MD 20746-2863 USA, Tel: 301-238-6624x6313; Fax: 301-238-3201; E-mail: email@example.com
Featured Artifact, Archaeology (publication of the Archaeological Institute of America), vol. 63, no. 6, Nov.-Dec. 2010, p 72.