Friday, 19 October 2012

Investigating Plant Fibres

A part of this project to conserve and investigate the Cook-voyage collections at the Pitt Rivers Museum is to attempt to identify the materials from which the objects are made.  Knowing what artefacts are made from can help us find out where they were collected.  Although the Catalogue of Curiosities gives us fairly good information about this, sometimes there is still confusion, as in entry No. 98. 'Nine different kinds of necklaces; together with three mother of pearl shells which hang on the breast.'  Although this entry appears in the section entitled 'The Friendly Isles' (Tonga) not all of the necklaces come from there - some, in fact, were thought to be from New Zealand. 

Information about materials comes from various sources - the Forsters sometimes mention what the objects they collected were made from.  Curators and researchers have added information over the years - but sometimes materials are very similar and only close observation under the microscope can distinguish them.  Plant fibres come into this category, which brings me back to the nine necklaces which are part of Forster No. 98.  

Nine necklaces, part of Forster No. 98

The necklaces are all made from beads of various kinds, threaded on cords made from vegetable fibre.  If the necklace is from New Zealand, the fibre will probably be from New Zealand flax (Phormium tenax - harakeke).  This plant did not grow on Tonga in the Eighteenth century - the Tongans used a plant in the nettle family, Pipturus argenteus (olonga) to make a fine cord, also used in the manufacture of fish hooks and nets.   

Samples consisting of a single fragment of fibre were taken from the cords of all of the necklaces.  The samples were dehydrated in ethanol, and then washed in toluene before being mounted on slides in Numount, a synthetic mounting medium intended as a replacement for Canada Balsam.   The samples need to be washed in toluene, which is the solvent for Numount, because ethanol would make the Numount go cloudy.  
Samples of loose fibres were taken from several Maori objects in the Cook-voyage collections, as examples of aged New Zealand flax fibres, and also from Tongan fishing hooks and a fishing net - likely to be samples of olonga.  

New Zealand flax fibres, x100

New Zealand flax fibres, x400

Comparison of the 'known' samples under the microscope, using crossed polars showed the the two fibres are quite distinct - the olonga fibre in particular has characteristic diagonal lines on the surface which may be a result of varying thicknesses within the cell wall. 

Olonga fibres, x100
Olonga fibres, x400

The samples taken from the necklaces could then be compared with the 'known' fibres.  The cords of those considered stylistically to come from Tonga were all made from olonga fibre, and those thought to come from New Zealand were made from harakeke.  One necklace was the subject of debate, but the fibre proved to be olonga, suggesting that it came from Tonga.

Fibres from necklace 1886.1.1575, x100

Fibres from 1886.1.1575, x400