Investigating approaches to the treatment and preservation of a collection of Egyptian limestone funerary stelae

ABSTRACT

This paper discusses the development of a treatment protocol and preservation guidelines for a collection of 211 limestone funerary stelae from the Roman Egyptian city of Terenouthis. The stelae, now at the University of Michigan’s Kelsey Museum of Archaeology, suffer from surface powdering, soluble salt activity, stone delamination, biological staining, and a peeling, darkened nitrocellulose coating. Analytical techniques including FTIR, portable XRF, XRD, specimen culturing, and DNA analysis were used to characterize the stone, confirm the presence of soluble salts, identify the coating, and determine the exact nature of the biological growths seen on many stelae. These data were used to investigate treatment approaches, including consolidation, stone stabilization, coating reduction, and biostain reduction. Desalination by poultice was also explored. Based on the results of testing, a criterion-based treatment protocol was developed. The protocol recommends treatment steps including consolidation with CaLoSiL NP25 nanolime, structural stabilization using a variety of B-72 applications, and coating reduction with acetone in different solvent carriers. Finally, environmental monitoring and scientific analysis were used to create a set of environmental guidelines for the collection’s long-term preservation.

RÉSUMÉ

Cet article traite du développement d’un protocole de traitement et de lignes directrices pour une collection de 211 stèles funéraires en calcaire provenant de la cité égyptienne romaine Térénouthis. Les stèles, maintenant conservées au Kelsey Museum of Archaeology de l’Université du Michigan, souffrent de pulvérulence de surface, de l’activité de sels solubles, du délitage de la pierre, de taches d’origine biologiques, et du pelage d’un enduit de nitrate de cellulose assombri. Les méthodes analytiques incluant l’IRTF, la FRX portative, la DRX, la culture d’échantillons et l’analyse d’ADN ont été utilisées pour caractériser la pierre, confirmer la présence de sels solubles, identifier la nature de l’enduit, et déterminer la nature exacte des croissances biologiques observées sur plusieurs stèles. Ces données ont été utilisées pour examiner des approches de traitement, incluant la consolidation, la stabilisation de la pierre, l’allègement de l’enduit et l’atténuation des taches d’origine biologique. Le dessalement par l’application de compresses a aussi été exploré. À partir des résultats des tests, un protocole fondé sur des critères a été développé. Le protocole recommande un traitement par étape incluant la consolidation avec la nanochaux CaLoSil NP25, la stabilisation structurelle utilisant une variété de méthodes d’application de B-72, et l’allègement de l’enduit à l’aide d’acétone sur différents supports. Finalement, un suivi environnemental et des analyses scientifiques ont été utilisés pour créer un ensemble de lignes directrices environnementales pour la conservation à long terme de la collection. Traduit par Isabelle Cloutier.

RESUMO

O artigo discute o desenvolvimento de um protocolo de tratamento e diretrizes de preservação para uma coleção de 211 estelas funerárias de calcário da cidade romano- egípcia de Terenouthis. As estelas, atualmente no Museu de Arqueologia de Kelsey da Universidade de Michigan, sofrem de pulverização superficial, atividade do sal solúvel, delaminação da pedra, tintura biológica e uma descamação, camada escurecida de nitrocelulose. Foram utilizadas técnicas analíticas incluindo espectoscopia infravermelho com transformada de Fourier (FTIR), analisadores portáteis de fluorescência de raios X (XRF), difração de raio X (XRD), cultura de espécimes e análise de DNA para caracterizar a pedra, confirmar a presença de sais solúveis, identificar o revestimento e determinar a natureza exata dos crescimentos biológicos observados em muitas estelas. Esses dados foram utilizados para investigar abordagens de tratamento, incluindo consolidação, estabilização da pedra, redução do revestimento e redução de manchas biológicas. A dessalinização por cataplasma também foi explorada. Com base nos resultados dos testes, foi desenvolvido um protocolo de tratamento baseado em critérios. O protocolo recomenda etapas de tratamento, incluindo a consolidação com nanolime CaLoSiL NP25, estabilização estrutural usando uma variedade de aplicações B-72 e redução de revestimento com acetona em diferentes suportes solventes. Finalmente, o monitoramento ambiental e a análise científica foram utilizados para criar um conjunto de diretrizes ambientais para a preservação a longo prazo da coleção. Traduzido por Cristina Antunes.

RESUMEN

Este artículo discute el desarrollo de un protocolo de tratamiento y guías de preservación para una colección de 211 estelas funerarias de la ciudad Romana Egipcia de Terenouthis. Las estelas, actualmente en el Museo Arqueológico de la Universidad de Michigan, sufren de pulverización de la superficie, actividad de sales solubles, delaminación de la piedra, manchas biológicas y un desprendimiento y oscurecimiento del recubrimiento de nitrocelulosa. Se usaron técnicas analíticas, incluyendo: FTIR, XRF portátil, XRD, cultivo de especímenes, y análisis de ADN, para caracterizar la piedra, confirmar la presencia de sales solubles, identificar el recubrimiento y determinar la naturaleza exacta de los crecimientos biológicos observados en muchas de las estelas. Estos datos fueron utilizados para explorar enfoques de tratamiento incluyendo consolidación, estabilización de la piedra, reducción del recubrimiento y reducción de las manchas biológicas. También se exploró la desalinización por medio de cataplasmas. Basado en los resultados de pruebas, se desarrolló un protocolo de tratamiento en base a criterios. El protocolo recomienda los pasos de tratamiento que incluye: consolidación con CaLoSiL NP25 nanocaliza, estabilización estructural usando una variedad de aplicaciones de B-72 y reducción del recubrimiento con acetona en diferentes portadores de solvente. Finalmente, se usaron monitores ambientales y análisis científicos para crear un conjunto de recomendaciones ambientales para la preservación a largo plazo de la colección. Traducción: Hilda Abreu de Utermolhen y María Esteva; revisión: Amparo Rueda de Torres.

KEYWORDS:

• Roman Egypt
• limestone
• stelae
• nanolime
• calclacite
• cellulose nitrate
• polychromy

Acknowledgements

The authors would like to thank Claudia Chemello and Terry Wilfong for their contributions to this project, and the Samuel H. Kress Foundation for its support. Scientific analysis and materials testing was carried out with the help of Tim James, Katherine Lazarus, Anja Schleicher, Cathleen Baker, and Joseph Weber.

Notes on contributors

Caroline Roberts is a conservator at the Kelsey Museum of Archaeology at the University of Michigan. She is a graduate of the Winterthur/University of Delaware Program in Art Conservation. As a graduate fellow, Carrie held internships at the Phoebe Hearst Museum of Anthropology, English Heritage, and the Worcester Art Museum. After graduating in 2011, Carrie pursued post-graduate fellowships at the Kelsey Museum of Archaeology, the J. Paul Getty Museum, and the Metropolitan Museum of Art. Carrie returned to the Kelsey Museum as a Conservator in 2014. Her interests include the conservation and preservation of stone artifacts and architecture in museum and field settings, the characterization of ancient polychromy, and preventive conservation. Carrie’s fieldwork experience includes seasons at Kaman-Kalehöyük in Turkey, Selinunte in Sicily, and El-Kurru in Sudan.

Suzanne Davis is the associate curator and head of conservation at the Kelsey Museum of Archaeology, University of Michigan. She is a graduate of New York University’s Conservation Center and is a fellow of the American Institute for Conservation (AIC). Archaeological conservation and site preservation are two of her primary interests, and she has provided conservation for excavations in the United States, Europe, Africa, and the Middle East.

LeeAnn Barnes Gordon is an associate conservator of objects at the Museum of Fine Arts, Boston. She holds a graduate degree from the Winterthur/University of Delaware Program in Art Conservation with a specialization in objects conservation. Previous positions include Graduate Intern at the Kelsey Museum of Archaeology, Sherman Fairchild Fellow in Objects Conservation at the Museum of Fine Arts, Boston, Project Manager for Conservation and Heritage Preservation of ASOR’s Syrian Heritage Initiative, and Assistant Conservator at the Harvard Peabody Museum of Archaeology and Ethnology.

Cathy Selvius DeRoo is a research scientist at the Detroit Institute of Arts. She earned her Ph.D. from the University of Michigan in biochemistry and was awarded a National Institutes of Health postdoctoral fellowship in biophysics. In addition to conducting analyses of the wide range of materials represented in the encyclopedic collections of the DIA, her research interests focus on the application of new techniques to the study of artists’ materials.

ORCID

Caroline Roberts http://orcid.org/0000-0002-6068-8455

Suzanne L. Davis http://orcid.org/0000-0001-6667-2203

Notes

1. XRF analysis indicated the use of iron-based earth pigments for the red and yellow colorants. Areas of black also had peaks for iron, but these may be due to surface dirt. XRD analysis characterized the green pigment as green earth.