Analytical Methods

The technique of taking paint cross-section samples, often less than a millimetre in size, has been employed for over a century. It is used to understand and identify the layers of materials employed to create artworks such as oil paintings, wall paintings and polychromes. Commonly the technique involves embedding these tiny samples in resins and polishing the resin to bring the samples to the surface enabling them to be viewed by light microscopy. Through magnification, these tiny samples are revealed as preparatory ground and paint layers and sometimes the underlying support, often a textile.

The use of this technique to study the construction of painted barkcloth has not been exploited before now. However, recent samples from a Hawaiian painted cloth (GLAHM E.667), part of the Hunterian Collection, have been embedded in an acrylic resin and viewed using light microscopy. Sampling is carried out in typical area where paint has been used to decorate the barkcloth fibre. In the cross-section sample shown here, it is clear that two paint layers have been used – a lighter and a darker red. The top darker red layer is extremely thin.

Colour photograph of a Hawaiian painted cloth from The Hunterian collection, reference GLAHM E.667. (copyright University of Glasgow)
A Hawaiian painted cloth from The Hunterian collection, GLAHM E.667

Colour photograph of a detail of the cloth, GLAHM E.667, with a box showing the red-painted area under investigation (copyright University of Glasgow)
Detail of GLAHM E.667; the box shows the red-painted area under investigation

Colour photograph showing a magnified image of a cross-section through the barkcloth. This shows that two paint layers have been used, a lighter and a darker red. The top darker red layer is extremely thin. (copyright University of Glasgow)
Magnified image of a cross-section through the barkcloth, showing two layers of red paint

Polishing a complete cross-section including the beaten bark poses problems that a cross-section of paint layers alone would not. The beaten bark is easily damaged if polished and so here a layer of resin still remains. The sample shown still has some resin on top of the sample which slightly impairs the quality of the image. Further developmental work is needed to improve the microscopic imagery from painted barkcloth cross-sections. This may include sandwiching them in a softer embedding material that can be cut revealing the layers without the need for polishing which can so easily damage the bark.

With a high quality embedded cross-section, further information can be obtained from the sample to shed light on the materials used. This could be done by using a variety of analytical instruments such as scanning-electron microscopy with energy dispersive X-ray (SEM/EDX) spectroscopy, Fourier transform infrared spectroscopy mapping. These methodologies can help identify the materials used to create the painted barkcloths.