AIC's 46th Annual Meeting

The Managing Collection Environments initiative at the Getty Conservation Institute focuses on research questions and practical issues relating to the control and management of collection environments in museums. Providing an evidence-base for the effect of environmental conditions on historic materials has long been a challenge for the conservation field, due to both the inherent complexity of the materials and the uncertainty in the mechanisms at play in environmentally-induced change. Understanding the mechanical properties of cultural heritage materials is a fundamental aspect of establishing effective preservation methods. Conventionally, the mechanical characterization of artists’ materials is performed by uniaxial or biaxial tensile testing and typically requires a large quantity of macro-sized samples. Having access to sufficient numbers of historic materials that satisfy this sample size requirement is impractical if not impossible when working with museum collections. As a consequence, the applicability of macro-mechanical testing in the conservation science can be limited. In contrast, small scale engineering techniques such as micro- and nano-indentation allow for the characterization of sub-millimeter samples taken from real works of art, rather than relying wholly upon much larger laboratory-prepared samples intended to mimic historic materials. These engineering techniques open a new perspective on the systematic analysis of the probabilistic distribution of mechanical properties of artists’ materials. They also allow for the analysis of ageing factors which can alter the mechanical properties of a material. The primary focus of this study is the application of micro- and nano-indentation to investigate the effect of an embedding process on the mechanical properties of cross-sectional samples of acrylic-based paint. As a precursor to the analysis of historic samples, a systematic investigation of embedded samples was performed to assess the role of sample size, surface roughness and structural compliance of the embedding resin. Material characterization was conducted at ambient laboratory conditions using an Ultra-High Resolution Nanoindentation Tester (Anton Paar) equipped with a Berkovich (three-sided pyramidal) diamond indenter. Load–displacement tests were carried out on embedded and free-film samples to evaluate the quasi-static and dynamic behavior of the acrylic-based paint to better understand its deformation response. Mechanical parameters which are used for describing the stiffness of a material, such as the elastic behavior of a material (storage modulus) and the ability of the material to deform under constant load (creep), were obtained for cross-sectional samples and compared with results for the acrylic free-film. Results indicate that instrumented indentation can be successfully used as a stepping stone towards an improved understanding of mechanical properties of embedded artists’ materials and, consequently, allow one to better define the conservation needs of art objects.