A FUSION OF ARCHAEOLOGY AND CONSERVATION: PAINTED CLAY-COVERED BASKETRY FROM THE AMERICAN SOUTHWEST
ABSTRACT—Conservators and archaeologists share an interest in technology. For the archaeologist, technology may be viewed as prehistoric problem solving. For example, technology enables constructions for shelters, food gathering, and keeping warm. For the conservator, technology illustrates artistry or craftsmanship during the manipulation of materials. Both the archaeologist and the conservator are aware, no doubt, that technological style reflects social choice. This article illustrates how the study methods of the conservator can extract and preserve, as well as clarify, the particular technologies presented in very fragmentary material remains and address some of the comparative and interpretive issues associated with prehistoric societies.
TITRE—Un exemple de fusion entre l'arch�ologie et la conservation: la vannerie couverte d'argile et peinte provenant du sud-ouest am�ricain. R�SUM�—Les restaurateurs et les arch�ologues cultivent un m�me int�r�t pour la technologie des objets. Pour les arch�ologues, la technologie incarne la r�solution de probl�mes aux temps pr�historiques. Ainsi les d�veloppements technologiques permirent de r�soudre de mieux en mieux des probl�mes vitaux comme la construction d'abris, la cueillette de nourriture et la protection contre le froid. Pour les restaurateurs, la technologie repr�sente une m�thode artistique ou artisanale dans l'�tape de la transformation de la mati�re. Les arch�ologues et les restaurateurs se rendent compte, sans doute, que le style de technologie adopt�e est un reflet d'un certain choix social. Cet article d�montre comment les m�thodes d'analyse utilis�es en restauration peuvent mener � la d�couverte, � la pr�servation et � la clarification de certains aspects technologiques qui ont surv�cu dans des artefacts tr�s fragmentaires, ce qui apporte de nouveaux �l�ments dans l'�tude comparative et l'interpr�tation des soci�t�s pr�historiques.
TITULO—Una fusi�n entre la arqueolog�a y la conservaci�n: cester�a del suroeste americano cubierta con cer�mica pintada. RESUMEN—Los conservadores y los arque�logos comparten un inter�s en la tecnolog�a. Para el arque�logo la tecnolog�a puede ser vista como una resoluci�n prehist�rica de problemas. Por ejemplo, la tecnolog�a permite la construcci�n de refugios, la recolecci�n de comida y mantenerse abrigado. Para el conservador, la tecnolog�a ilustra destreza manual o art�stica durante la manipulaci�n de los materiales. Sin duda, tanto el arque�logo como el conservador est�n conscientes de que el estilo tecnol�gico refleja elecciones sociales. Este art�culo ilustra c�mo los m�todos de estudio del conservador pueden extraer y preservar, as� como aclarar, las tecnolog�as particulares presentes en los remanentes muy fragmentados de material, y abordar algunos de los aspectos interpretativos y comparativos asociados con sociedades prehist�ricas.
Incorporating the discipline of professional conservation into the process of archaeological fieldwork in the American Southwest is both unusual and relatively recent. Complex archaeological investigations often include multicomponent sites (such as architecture, agriculture, and activity specialization) and analysis representing a wide range of specialist activities. Typical areas for grouping the results of specialist studies may include chronological, environmental, osteological, and artifact analyses.
Although sometimes critical to the excavation process, conservation research has generally been utilized as a separate activity that is exclusive to the traditional analytical studies required in professional archaeology. More often, the interpretive observations of conservators are received during the process of postexcavation care when the artifacts have been accessioned and cataloged into a museum collection. This stage is usually long after the archaeological investigation and written interpretation phases have been completed.
Typically, only certain artifacts (special, unique, discussed or illustrated in the archaeological site report) are selected for individual museum accessioning and cataloging. The remainder may reside in bulk form as part of a repository collection. The technical observations made by the conservator about the objects during examination, cleaning, stabilization, storage, or exhibition tend to remain isolated in conservation laboratory files and are rarely incorporated back into the academic body of knowledge regarding the archaeological investigation whence they came.
Of course, there are some exceptions to this situation, and many conservators have found great satisfaction in the process of offering new skills, tools, and techniques to the recovery of finds. In fact, conservators can offer substantial additional information if they are included in the excavation and the interpretation phases of the archaeological process. This contribution has particularly applied when the excavation conditions for very fragile and fragmentary finds can be controlled through the excavation of a block lift back in the conservation laboratory.
Successful collaborations linking an archaeological excavation, conservation, and the interpretation of the archaeological finds include this story of three clay-covered basketry vessels with painted decorations recovered near Punkin Center, Arizona, in 1995 (Odegaard and Crawford 2001) and an armband made with similar technology recovered near Globe, Arizona, in 1997 (Odegaard, forthcoming). Together, these objects illustrate the benefits of conservation research in the interpretation phase of an archaeological investigation. Obtaining accurate and complete information pertaining to funerary objects is of particular importance due to the recent national and state laws regarding timely returns for reburial.
2 EXAMINATION OF THE CLAY-COVERED BASKETRY OBJECTS
Initially archaeologists from the Center for Desert Archaeology, a contract archaeology firm in Tucson, Arizona, contacted the Arizona State Museum (ASM) for advice regarding the stabilization of a unique clay-covered basket excavated from a Salado site in the Tonto Basin of central Arizona (Salado culture is identified as the cultural period from A.D. 1150 to 1450). Archaeologists had excavated a complete vessel consisting of a clay coating and painted decoration. Fearing that its fragile state would not withstand the lifting process, they consolidated the clay surfaces. Unfortunately, the surface was not as weak as the structure, and the vessel broke into many pieces during the excavation process. A second clay-coated basketry object had been partially excavated when the archaeologists decided to protect the structure and remove it as a partial block (fig. 1).1 A third object was left intact as an entire “block lift” mass. These objects were brought to the Arizona State Museum conservation laboratory for study. The primary constraints of this project included a limited amount of time before reburial and the stipulation that no materials be added or destroyed during the study.
Clay-covered basketry objects with painted decorations are extremely rare in the archaeological record of the American Southwest. Archaeologists have traditionally regarded the random fragments as exotic elements and generally devote little more than a sentence or two to their occurrence. Several notable Southwest archaeologists have reported the presence of clay-covered basketry fragments during archaeological excavations. A complete bibliographic list of these references appears in Odegaard and Hays-Gilpin (forthcoming).
Block lift of clay-covered basketry vessel 2 before excavation in the conservation laboratory
Determining the complete nature of all the technologies present in these objects was difficult due to their fragmentary and friable state of preservation. It was obvious that a thorough collection of data would be necessary for comparing these examples with known museum objects and samples reported in archaeological literature. Conservators Nancy Odegaard and Matthew Crawford utilized microscopy, chemical spot-testing techniques, and analytical techniques to gather and record information on a chart.
The conservation study began with a close examination of the layering or sandwichlike nature of the clay covering, the woven basketry impressions left in the clay covering, and the decorative use of pigments and painted designs (fig. 2). Initially, the general lack of basketry impression in one example suggested the possibility that another support material, such as leather, had been used to form the structure. A small fragment of the layered structure was opened to reveal the interior surface of the clay covering, where a chemical test for the presence of protein was used under a microscope. The Biuret test determines the presence of proteins if the copper (II) sulfate reagent solution forms a violet color (Odegaard et al. 2000, 144–45). The results with this test were negative, so a test for the presence of cellulose from within the sealed and layered sandwichlike structure was made. One test for the presence of cellulose includes the use of pyrolysis in the presence of orthophosphoric acid to form a gas that reacts with an aniline acetate reagent to give a pink spot (Odegaard et al. 2000, 160–66). This test resulted in a positive reaction, so the search for evidence of any remaining basketry structure using a stereo-zoom microscope continued until a faint impression was found.
Detail from Punkin Center clay-covered basketry object 2 illustrates the layering or sandwich-like nature of the clay covering. The woven basketry impressions are left on the inside of the clay layers.
A laboratory excavation of the soil block provided more complete preservation of the decorative areas and facilitated the process of taking comparable measurements of the woven impressions. Because the archaeologists had not attempted a complete field excavation of the third object, its original shape could be maintained through the use of more carefully controlled excavation techniques and the placement of strategic supports. The ability to examine the objects during the excavation also enabled more accurate documentation of the vessels' form (bowls), orientation in situ (both upright and inverted), overall measurements, wall-thickness measurements (ranging from 0.5 to 1.5 mm), weave structure (single-rod close coil), weave direction (to the left), workface, and Munsell notations for the clay and pigment colors (azurite, malachite, limonite).2
Some of the common characteristics previously observed on painted objects in the Southwest include color areas that tend to be separated by definite lines, colors that are not blended or mixed, and paints that are usually applied in uniform thickness (Odegaard 1998, 260). The basic approach to painting technology involves the use of ground pigments and an adhesive binder suspended in a liquid vehicle to form a dispersion. As the vehicle evaporates, the binder holds the pigment particles in place. Fine and uniform grinding ensures that the pigments remain evenly suspended throughout the vehicle so that sufficient color may be seen. In general, the ratio of pigment to binder concentration, as well as the amount of vehicle used to apply the paint, determines how matte or glossy the paint appears and how well it covers the surface when dry. Excess vehicle produced weak paint with poor covering power on one of the basketry objects. Generally, the paint technology on these clay-covered basketry objects includes the use of fine-grained pigments of even density, good application control, and lasting adhesion (fig. 3). On clay-covered basketry object 1, the quality of painting suggested that the artist was low on materials or did not understand the technology well, while the application of the paint suggests that the work was done in haste or that the artist lacked the skill demonstrated in the other examples.
Detail of a loose fragment from Punkin Center claycovered basketry vessel 3 illustrates the decorative use of pigments and painted designs.
A loose surface sample from another basketry object was analyzed by Fourier transform infrared reflectometry (FTIR) to determine the presence of organic binders in the paint, and none were identified.3 While it is possible that pigments suspended in liquid alone could adhere to the porous clay surface without the use of a binder, it is also likely that any organic binder (it would have been a small amount to produce the matte appearance) would have degraded over time. Another sample was analyzed by scanning electron microscope–energy dispersive spectrometry (SEM-EDS) to semiquantitatively confirm the identification of pigments previously identified by polarized light microscopy and chemical spot tests.3
(l-r) ASM object #GP46711 from the Rye Creek Ruin, ASM object #GP12601 from the Gila Pueblo Ruin, and Punkin Center clay-covered basketry object 3 are claycovered basketry bowls that had not been analyzed or published prior to these studies.
Detail from ASM object #GP46711 from the Rye Creek Ruin shows preservation of basketry stitch structure below clay covering and painted design.
Once the technical data were recorded for each of the clay-covered basketry objects, they were compared with cataloged examples in the Arizona State Museum collection (fig. 4). A nearly complete example from the Rye Creek Ruin (located to the north of the Punkin Center site) included the unusual use of a blue copper carbonate–based clay to cover the basketry (fig. 5). The biocidal properties of this clay preserved much of the actual basketry fiber, revealing an extensive amount of stitch detail. Another example from the ASM collection was from the Gila Pueblo Ruin (located to the south of the Punkin Center site). This example revealed areas of exposed foundation material and also offered the possibility of seeing the effects of a previous consolidation process on the original color and texture of the painted surface (fig. 6). The details on these more intact specimens facilitated the search for impression details on other sample fragments where no actual fibers remained. After the examination of similar specimens, archaeological field notes, published reports, and additional groups of cataloged fragments were reviewed. Most examples illustrated the use of remarkably similar basketry technology but different coating materials or slightly different pigments and design motifs.
Detail from ASM object #GP12601 from the Gila Pueblo Ruin shows preservation of basketry foundation material and consolidation of the painted surface.
3 ANOTHER FORM OF CLAY-COVERED BASKETRY OBJECT
In 1997 another clay-covered basketry object was recovered from outside the town of Globe, Arizona. Based on the findings from the Punkin Center study, archaeologists from Archaeological Consulting Services requested assistance from conservators. This object was delivered as a partially excavated fragment located in the interior of a ceramic bowl. Because the painted surface was allowed to dry quickly and was left unprotected during the excavation and during the months prior to conservation, it had become a thin, dry crust over a loose gravel matrix (fig. 7). All of the remaining basketry, coating, and pigment materials were extremely weak and fragile. The request included removal of the artifact, examination, and determination of technology without the use of consolidants or other additives.
Information such as stitch size, count, stitch splitting, and other details was observable in the fragmentary bits. However, many details regarding the type of foundation (rod count and arrangement) and how the piece was finished (length and style of taper, knot, or blunt end) could be determined. Details about the clay coating and pigments could be compared to the other fragments. Difficulties in reconstructing the original design and shape of the basket led to a more complete review of the context of the burial. Based on its location in the burial, the lack of any base material, and the orientation of the design elements, the object appeared to be an armband. Fragments from armbands were reviewed, and other published accounts, field notes, and reports were consulted. Technological comparisons with unpublished specimens from several museums and a review of the archaeological literature for comparable technologies were undertaken. One example had a nearly identical design, and other references indicate that decorated armbands existed at numerous sites in the American Southwest. A complete bibliography of known armband comparisons and a comparative table of traits based on published accounts and examined specimens appear in Odegaard and Hays-Gilpin (forthcoming).
The clay-covered basketry armband from the Murray Wash site shown as delivered to the conservation laboratory in a ceramic bowl of Salado Red type
Also, armbands worn near the elbow are often depicted on many ancient and modern Puebloan carvings and in drawings or paintings as part of the ceremonial costume. A variety of materials including wood, metal, leather, cloth, and fur may be used as the substrate with paint or turquoise and other stones applied for decorations.
To date, about 30 painted clay-covered basketry containers and armbands recovered from the American Southwest have been identified. They are rare, delicate, and generally fragmentary. They appear in sites spread widely in the region. It is unlikely that they served a utilitarian purpose. When examples are reported in sufficient detail, the evidence suggests that they accompany elaborate burials dating from the mid-1200s to the late 1300s. In several examples, it appears that the basketry had already undergone some attrition or wear prior the clay coating. In most of the known examples, the painting illustrates the use of quality materials and fine artistry. While the colors and designs used on these objects vary some-what, there are some common trends. Parallel bands worked into zigzags, nested triangles, and radiating lines are typical on most examples. Within the burial features, the placement of these objects near the head or on the upper body and inside ceramic bowls is typical.
Initially, project archaeologists viewed these objects as exotic and without significant comparison in the archaeological record. Due to their extremely fragile and fragmentary state of condition, the archaeologists expected that little could be revealed through the technical analysis process. However, the application of techniques and methodologies used in the discipline of conservation to recover, examine, and analyze the painted clay-covered basketry did result in important ethnological information. Aspects of the interpretive findings in the multicomponent sites seem to be comparable and consistent with those of other artifact analyses, which included ground stone, flaked stone, ceramics, shell, bone tools and ornaments, wooden objects, and worked stone. Additionally, several links to observations identified in the chronological, osteological, and environmental analysis have also been noted. Finally, ongoing studies indicate that a close examination of the paint technology utilized on these objects may be considered very important because it required a planned sequence of actions. Sequences may be learned by observation or by extensive experimentation with the goal of obtaining clear colors, even density, edge control, and lasting adhesion of the paint to the surface. Odegaard and Hays-Gilpin (forthcoming) suggest that the remarkably consistent and labor-intensive technology utilized in the manufacture of painted clay-covered basketry objects may provide a line of evidence for establishing cultural affiliation among groups that are separated by time and space. This supports the notion that elite status in the Southwest was based, in part, on the control of specialized knowledge and ritually linked items.
The analysis of multiple-component artifacts such as painted clay-covered basketry objects is well suited to the application of a conservation-based study. The process illustrates the use of the conservation discipline beyond the application of artifact treatment and clarifies its value in the written interpretation phase of an archaeological investigation. These studies have alerted archaeologists to several previously unknown aspects of the conservation discipline. As a result, the role of the conservator has been better understood and utilized.
1. Clay-covered objects with painted decorations are usually found in burials of people with high status. Among the artifacts discovered during the laboratory excavation of this basketry vessel were 2 bone wands or hair ornaments, 2 carved shell birds, more than 100 turquoise beads, 12 worn pieces of stone, and 1 square stone pendant.
2. Munsell color chips are squares of solid color identified by hue/value/chroma. The Book of Color matte collection includes 1,270 color chips on 40 charts in a notebook. Under proper illumination and viewing conditions, the Munsell chips are compared to samples, thereby providing a reference point. The color notations allow for color comparisons among viewed specimens. The charts are available from GretagMacbeth at (800) 622–2384 or www.munsell.com
3. Dale Kronkright, conservator for the Conservation Laboratory of the Museum of New Mexico in Santa Fe, N. Mex., performed the FTIR analysis using a Nicolet Protegy 460 on a loose sample from clay-covered basketry vessel 3. Dr. Karen Adams, ethno-botanist, and Dr. Joe Stewart, chemist, at Lakehead University, Canada, performed SEM-EDS using a Hitachi 570 with Link Isis software.
Odegaard, N.1998. An investigation of the nature of paint on wood objects in the indigenous Southwest of North America. In Painted wood: History and conservation, ed. V.Dorge. Washington, D.C.: FAIC. 255–67.
Odegaard, N. Forthcoming. Perishable remains with human burials: A clay-covered painted basketry object from the Murray Wash Site. In Settlement history along Pinal Creek in the Globe Highlands, Vol. 2, Human remains and mortuary patterns, ed. D. E.Doyel and T. L.Hoffman.Cultural Resources Report 112. Tempe, Ariz.: Archaeological Consulting Services.
Odegaard, N., S.Carroll, and W.Zimmt. 2000. Material characterization tests for objects of art and archaeology. London: Archetype Books.
Odegaard, N., and M.Crawford. 2001. Baskets and other non-ceramic containers. In Life and death along Tonto Creek, ed. J. J.Clark and P. D.Minturen. Anthropological Papers 24. Tucson: Center for Desert Archaeology. 519–29.
Odegaard, N., and K.Hays-Gilpin. Forthcoming. Technology of the sacred? Painted basketry in the Southwest. In At the millennium: Change and challenge in the greater Southwest, ed. M.Warburton and C. M.Cameron. Boulder: University of Colorado Press.
NANCY ODEGAARD has 25 years' experience with archaeological collections in museums and excavations. She holds a B.A. (University of Redlands), M.A. (George Washington University), Certificate in Ethnographic and Archaeological Conservation (Smithsonian Institution), and Ph.D. (University of Canberra). She currently heads the conservation laboratory at the Arizona State Museum at the University of Arizona and works with ethnological and archaeological collections, repository collections, and various excavation projects. Address: Arizona State Museum, University of Arizona, Tucson, Ariz. 85721