Analysis

The technical analysis component of the project drew on detailed object-based analysis to investigate the materials and processes involved in making barkcloth.

Fibre identification

Identifying the plant species used to make barkcloth has always been challenging – the fibres are flattened by the beating process so can’t be identified by looking at them through a microscope, as is usually done with plant fibres. Dr Margaret Smith, our Scientific Research Associate, developed a new technique for barkcloth species identification using Fourier transform infrared spectroscopy with attenuated total reflection (ATR-FTIR) and principal component analysis (PCA) to differentiate between historic barkcloths.

A set of 22 contemporary and 79 historic cloths was analysed to develop this methodology. In this preliminary study of contemporary and historic barkcloth, multivariate analysis of FTIR spectra in the 1200–1600 cm−1 region has been shown to be useful in grouping historical barkcloths originating from different species. PCA analysis identified three groups for the historical cloth with the loading plots highlighting where the differences between the FTIR spectra are predominant for each principal component. In addition, employing hierarchical cluster analysis (HCA) to analyse the data identified cloths that have a close relationship to each other and showed a clear link between the cloths that are thought to be composed of mixed fibres. This shows the usefulness of this statistical technique to historic bark cloth analysis.

The feel of barkcloth is often as important as visual clues in deciphering its material and manufacture, but we found that visual and textural differences in the cloths are often more dependent on the processing method than the fibre type. We also found that comparisons between historic and contemporary barkcloth should be treated with caution, as tests on old and new fibres weren’t always corroborative.

Colour photograph showing Margaret Smith, the barkcloth project scientific researcher, conducting pXRF analysis of a barkcloth together with Susanna Harris ,a colleague from the Archaeology Department (copyright University of Glasgow)
Margaret Smith conducting portable X-ray fluorescence (pXRF) analysis of a barkcloth together with Susanna Harris , a colleague from the Archaeology Department

Trialling other techniques

Genome sequencing (DNA research) and scanning electron microscopy (SEM) were also trialled as useful comparative techniques. DNA research has identified relevant marker sequences and successfully matched unknown samples against known samples although the large sample size required (around 1cm2) is prohibitive for many artefacts. We did however confirm that light microscopy in combination with staining, traditionally used for plant identification, is not reliable. We also found that low-level stereomicroscopy and high-level light microscopy were useful tools to tell us about the condition of the fibres, their characteristics and the methods of applying colourants.

Analysing the colourants used on barkcloth

Dye and pigment analysis is rather more straightforward though it’s rare that large numbers of barkcloths are examined. Samples from 54 historic cloths were analysed using high performance liquid chromatography (HPLC) for organic sources and X-ray fluorescence (XRF) for inorganic pigments. Interestingly, and in line with complementary research carried out at the British Museum (Tamburini et al., 2019), despite the numerous colourant sources for the red, brown and yellow shades listed in the many historic accounts of barkcloth making, only four plant sources (principally noni, tannin and turmeric with a small amount of madder) and one pigment, iron ochre, were identified. However we need to set this in context: cloths in European collections were collected in particular places at particular times and they represent a tiny proportion of all cloths made in Oceania in past centuries.

Value of an interdisciplinary approach

Nonetheless, this result demonstrates that the historical literature needs to be treated critically, like any other source. The research also showed that contemporary barkcloth practice cannot be used uncritically as a guide for understanding artefacts made in the past – analytical investigation of historic and contemporary materials was not always corroborative – confirming the value of an interdisciplinary approach.