Artworks and Cultural Heritage Materials: Using Multivariate Analysis to Answer Conservation Questions

The key concepts of data management systems that are applied to combinatorial and high-throughput chemical systems may also be applied to assist with answering questions involving conservation and cultural heritage materials. The chapter begins with an overview of conservation and explains what conservation is, why it is important, and how it is implemented for the preservation of cultural materials. The inherent value of most cultural materials imposes certain limitations on the types of analytical approaches that may be employed during analysis. An emphasis on noninvasive, nondestructive or microsampling is important to minimize the impact of analytical methodologies upon the artefact that is being studied, and multivariate approaches can maximize the information that may be derived from an analytical technique. In a review of nondestructive analysis and testing of museum objects, Adriaens (Spectrochimica Acta Part B: Atomic Spectroscopy 2005, 60 (12), 1503–1516) reiterates an important conservation principle, i.e. that we should aim for the maximization of information with a minimization of consumed volume of sample. Consistent with other applications in the fields of remote sensing, analysis of metadata and high-throughput or combinatorial approaches, methods for visualization of complex data, multivariate analysis and processing of high volumes of data, advanced data compression using data transformation and cluster analysis for data exploration and mining or pattern recognition are utilized. Cultural heritage studies are often directed at specific compositional and sample relational questions, due to the fact that little documentation about the specific preparation of the artefact exists. Also, because the analyst is dealing with natural materials with inherent sample variability, there is often little a priori knowledge of the sample set, so unsupervised approaches are useful for data exploration. This chapter presents a number of case studies that are used to illustrate the use of multivariate analysis (MVA) and chemometric approaches in studies of cultural artefacts and works of art. By deriving correlations, trends, clusters trajectory and anomalies or outliers in nonspatial and spatial data sets, a number of specific conservation issues are addressed. Firstly, in a multi-year study, the surface mineralogical profile of Australian Aboriginal Rock Art petroglyphs was examined using visible–near infrared reflectance spectroscopy and principal component analysis (PCA). A Cypriot pottery collection repaired with adhesives was studied using Fourier transform infrared (FTIR) spectroscopy and further historical information was revealed using PCA. The pigments and binding media used to decorate an Egyptian sarcophagus were examined with Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray absorption near-edge structure spectroscopy (XANES), and attribution studies of an Italian renaissance painting and imaging of ochre pigments using X-ray fluorescence (XRF) elemental imaging are presented.