Adaptation of a Standard Industrial Peel Test for Testing Consolidants in the Conservation Studio

ABSTRACT

Adhesives and consolidant strength play a major role in many conservation treatments. In industry, adhesive strength is often determined using standardized tests including 90° peel tests. However, not all conservation studios have or can afford mechanical testing equipment for such tests, although it is often readily accessible at third-party facilities. For a university conservation project, an international standard 90° peel test was modified to study the adhesive strength of consolidants for zinc white paints. Consolidants were applied to painting canvas strips, which were then adhered to zinc white paint layers on glass supports. The strips were peeled downward by continually adding fine sand to a cup attached to the end of the canvas strips. Video recordings were made of the continual loading and sudden stepwise extensions of the peeling samples, so that step-wise force - peel length curves could be plotted for each specimen. The data combined with examination of the peeled surfaces provided important qualitative information over strength and toughness (ductility/brittleness) for comparing the tested consolidant-zinc white systems. The adapted peel test is therefore a valuable method for testing adhesives and consolidants in the conservation studio. However, one must avoid overinterpreting the results, since consolidant selection depends on more factors than just mechanical properties.

RÉSUMÉ

La force des adhésifs et consolidants joue un rôle majeur dans de nombreux traitements de restauration. En industrie, la force d'un adhésif est souvent déterminée en utilisant des tests standardisés tels que des tests de pelage à 90°. Toutefois, tous les laboratoires de restauration n'ont pas accès ou n'ont pas les moyens de payer des dispositifs de tests mécanique pour de tels tests, bien qu'ils soient accessibles dans certaines institutions tierces. Pour un projet de restauration dans une université, un test de pelage standard international à 90° a été modifié afin d'étudier la force d'adhésion de consolidants utilisés sur peintures au blanc de zinc. Les consolidants ont été appliqués sur des bandes de toile, elles-mêmes ensuite adhérées aux couches de peintures de blanc de zinc sur des supports en verre. Les bandes ont été pelées vers le bas par le biais d'ajout continu de sable fin dans un récipient attaché à une extrémité des bandes. Des enregistrements vidéo ont été effectués afin de documenter le chargement en continu et les extensions des échantillons de pelage se produisant soudainement par étapes. De cette façon, les courbes de la force de pelage par étapes ont pu être tracées pour chaque échantillon. Les données combinées avec l'examen des surfaces pelées ont fourni des informations qualitatives importantes sur la force et la dureté (ductilité et fragilité) permettant de comparer les systèmes consolidant-blanc de zinc testés. Le test de pelage adapté est donc une méthode efficace pour tester des adhésifs et consolidants en laboratoire de restauration. Toutefois, il faut éviter de surinterpréter les résultats car le choix d'un consolidant se base sur davantage de facteurs que les propriétés mécaniques seules. Traduit par Marie-Hélène Nadeau.

RESUMO

Os adesivos e a resistência do consolidante desempenham um papel importante em muitos tratamentos de conservação. Na indústria, a força adesiva é frequentemente determinada usando testes padronizados, incluindo testes de aderência a 90°. No entanto, nem todos os estúdios de conservação têm ou podem comprar equipamentos de testes mecânicos para essas avaliações, embora muitas vezes eles sejam facilmente acessíveis em instalações de terceiros. Para um projeto de conservação universitário, um padrão internacional de teste de aderência a 90° foi modificado para estudar a resistência adesiva de consolidantes para tintas branco de zinco. Os consolidantes foram aplicados em tiras de tela de pintura, que foram então aderidas a camadas de tinta branco de zinco sobre suportes de vidro. As tiras foram delaminadas para baixo adicionando continuamente areia fina a um recipiente preso à extremidade das tiras de lona. Foram feitas gravações de vídeo do tensionamento contínuo e de extensões graduais repentinas das amostras delaminadas, de modo que a força gradual - curvas de duração da aderência - pudessem ser calculadas para cada amostra. Os dados combinados com o exame das superfícies delaminadas forneceram informações qualitativas importantes sobre resistência e tenacidade (ductilidade/fragilidade) para comparação dos sistemas consolidante/branco de zinco testados. O Teste de Aderência adaptado é, portanto, um método valioso para testar adesivos e consolidantes no atelier de conservação. No entanto, deve-se evitar superestimar os resultados, pois a seleção do consolidante depende de mais fatores do que apenas propriedades mecânicas. Traduzido por Caroline Lodi.

RESUMEN

La fuerza adhesiva y consolidante juega un papel importante en muchos tratamientos de conservación. En la industria, la fuerza adhesiva a menudo se determina mediante pruebas estandarizadas que incluyen pruebas de cizallamiento a 90°. Sin embargo, no todos los talleres de conservación tienen o pueden costear equipos mecánicos para tales pruebas, si bien a menudo son fácilmente accesibles como servicios contratados. Para un proyecto de conservación de la universidad, se modificó una prueba de cizallamiento estándar internacional a 90° para estudiar la fuerza adhesiva de los consolidantes para pinturas de blanco de zinc. Los consolidantes se aplicaron en las tiras de lienzo pintadas que luego se adhirieron a capas de pintura de blanco de zinc sobre soportes de vidrio. La fuerza de cizallamiento en las tiras fue ejercida hacia abajo por medio del agregado continuo de arena fina a un vaso unido al extremo opuesto en las tiras de lienzo. Se realizaron grabaciones de vídeo de la carga continua y de las extensiones escalonadas repentinas de las muestras de cizallamiento, de modo que la fuerza escalonada – curvas de longitud de cizallamiento pudieran trazarse para cada ejemplar. Los datos, combinados con el examen de las superficies peladas, proporcionaron importante información cualitativa sobre la resistencia y tenacidad (ductilidad/ fragilidad) para comparar los sistemas analizados de blanco de zinc y consolidantes. Por lo tanto, la prueba de cizallamiento adaptada es un método valioso para probar adhesivos y consolidantes en el taller de conservación. Sin embargo, se debe evitar la interpretación excesiva de los resultados, ya que la selección del consolidante depende de otros factores además de las propiedades mecánicas. Traducción: Soledad Tancoff; revisión: Amparo Rueda, Patricio Cevallos Salas, e Irene Delaveris.

KEYWORDS:

• adhesives
• consolidants
• flaking
• mechanical testing
• peel-test
• strength

Acknowledgements

The work discussed in this paper was part of a Master’s project conducted in 2018 by the first author in the Conservation and Restoration group of the Faculty of Humanities, University of Amsterdam (Kollaard 2018).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 Note that if the specimen fails in the rigid adherend, the results only say that the adhesive is stronger than the adherend. The results then say nothing about how strong the adhesive is.

Additional information

Notes on contributors

Noa Kollaard

Noa Kollaard trained as paintings conservator at the University of Amsterdam. She obtained her bachelor's degree in Art History in 2015, followed by a two-years master's in Conservation and Restoration of Cultural Heritage, where she specialized in paintings conservation. After graduating in 2017, she continued with a two-year post-master program in conservation and restoration at the University of Amsterdam. This program included internships at the Stichting Restauratie Atelier Limburg in Maastricht and at the conservation studio of the Mauritshuis in The Hague. After completion of the post-master program, she started working as a freelance paintings conservator. She currently works on various conservation projects for private conservation studios throughout the Netherlands.

W. (Bill) Wei

Dr. W (Bill) Wei (1955) is a senior conservation scientist in the Research Department of the Cultural Heritage Agency of the Netherlands (RCE - Rijksdienst voor het Cultureel Erfgoed). He has a BSE in mechanical engineering from Princeton University (1977) and a PhD in materials science from the University of Illinois at Urbana-Champaign (1983). Before working in the cultural heritage field, he spent almost twenty years in industrial research and development in the areas of advanced materials, mechanical properties, fracture mechanics and fatigue, and corrosion. He has been conducting research into and consulting on the effects of vibrations and mechanical stresses on the condition of fragile works of art and cultural heritage for more than twenty years. He has recently retired from the RCE and is now an independent consultant. Address: Cultural Heritage Laboratory, Cultural Heritage Agency of the Netherlands, Amsterdam, Netherlands. Email: [email protected].