Understanding consolidants on harakeke fibres using Raman microscopy: Implications for conservation

Abstract

Abstract Many customary Māori textiles are produced from harakeke fibres (muka) which are extracted from New Zealand flax (Phormium tenax) and some are dyed with paru (black) iron-tannate dyes. These tannate-dyed textiles degrade via iron catalysed oxidation and acid catalysed hydrolysis. To mitigate this degradation, conservators can potentially use various types of natural and synthetic consolidants; however, there is a lack of systematic study of the interaction between muka and consolidants. As part of a larger research project investigating the efficacy of six consolidants for treatment of deteriorated black-dyed muka in Māori textiles, the penetration of different consolidants applied to muka was investigated. By using Raman microscopy combined with chemometrics, this study was able to aid in selection, and concentration of, consolidants for use in the larger project. Six different consolidants; sodium alginate, zinc alginate, Paraloid B-72™ (ethyl-methyl methacrylate), TRI-Funori™ (seaweed extract, polysaccharide), Klucel G™ (hydroxypropyl cellulose), and Methocel A4C™ (methylcellulose) were applied at three concentrations (0.5, 1.0, and 2.0% w/v) to muka. The consolidated samples were sectioned and analysed using Raman microscopy mapping with a 532 nm incident laser. Relative intensity levels of the signals from the fibres and the consolidants were used to generate maps of the chemical composition across the fibre. Univariate analysis (with unique band integrals) and multivariate analysis (true component analysis) of the chemical images was able to distinguish the penetration pattern of consolidants, Paraloid B-72™, TRI-Funori™, and Klucel G™ into the fibres. The analysis of Methocel A4C™ was not possible because the spectral characteristics were too similar between the two. Sodium and zinc alginate consolidated samples tended to burn and no useful data could be collected. The consolidants accumulated in the intercellular spaces/middle lamella of the fibre's morphological structure and did not appear to penetrate into the fibre cell walls. The results from the study demonstrated the usefulness of Raman microscopy for understanding the properties and behaviour of consolidants applied to important cultural materials.