Monday, 17 December 2012

Plant Identification, and a 'fine and beautiful braid of human hair'

Last week, Caroline Cartwright from the Department of Conservation and Scientific Research at the British Museum came to visit us at the Pitt Rivers.  Caroline is an expert in the identification of plant fibres, and she will be carrying out some ID work for the Conserving 'Curiosities' project.  

In a previous blog post I mentioned that the investigation of the materials from which objects are made can give us information about where they come from - even though the Forster collection in particular is relatively well documented, there is still confusion about this.  Even when we know for sure where an object comes from, like this unique barkcloth from Easter Island (Rapa Nui), some of the materials still remain unidentified.  

1886.1.1250 Barkcloth, Easter Island

The barkcloth has decorative bands of plant material sewn across each end - said to be a rush that grows in the bottom of the extinct volcano (Rano Kau) on Easter Island.  A cord made from plant fibre was used to sew the layers of barkcloth together at intervals - almost like quilting.  

1886.1.1250 Detail of stitching and fibre
Other material that Caroline will look at includes plant fragments found in this headdress.  

1886.1.1685 Tamau Headdress, Tahiti

This is Forster No. 40, 'The Tamow, or headdress of plaited hair.'  Considered to be a 'lost' Forster object, it was found under the bindings of the Tahitian Mourner's costume.  

The tamau as found on the headdress of the Mourner's costume

The tamau was made of many metres of plaited human hair, made to form a continuous length.  It was worn by women as they danced, and the centre was filled with flowers.  

A young woman of Otaheite Dancing, after John Webber

George Forster, in 'A Voyage Round the World', saw a dance performance in the Society Islands in September 1773. He talks about the dress of the dancers, which included 'Poyadua (Poedua), the fair daughter of the chief Orea'…

'The neck, shoulders and arms were left uncovered, but the head was ornamented with a kind of turban, about eight inches high, made of several skains of plaited human hair, which they call tamow.  These being laid above each other in circles, which enlarged towards the top, there was a deep hollow left in the middle, which they had filled up with a great quantity of the sweet-scented flowers of the (gardenia) cape jasmine.  But all the front of the turban was ornamented with three or four rows of a small white flower, which formed little stars, and had as elegant an effect on the jetty black hair as if it had been set with pearls.'

William Ellis also described a group of dancers on Tahiti in 'Polynesian Researches', published in 1831.

'The daughters of the chiefs, who were the dancers on these occasions, at times amounted to five or six, though occasionally only one exhibited her symmetry of figure, and gracefulness of action.  Their dress was singular, but elegant.  The head was ornamented with tamau, a fine and beautiful braid of human hair, wound around the head in the form of a turban. *  A triple wreath of scarlet, white and yellow flowers, composed of the aute, the fragrant gardenia, or Cape jessamine, and the baslaria laurifolia, tastefully interwoven, adorned the curious head-dress.

* Mr Barff, to whom I am indebted for the principal part of this account, procured a head-dress of this kind, containing one hundred fathoms of the finest braided human hair.'  

One hundred fathoms is about 180m.  It is likely that the tamau in the Pitt Rivers collection contains closer to 1000m of hair.  

Fragments of plant material were taken from this and several other objects, and we hope that with Caroline's help some of the questions that people have been asking about the Cook-voyage collections for several hundred years might finally be answered. 

Thursday, 6 December 2012

Pesticides on Museum Objects

Part of the Cook-Voyage project at the Pitt Rivers is to look at the question of pesticide residues on objects from the collections.  Chemicals have always been applied to objects in museum collections to protect them from pests, mainly insects, which can cause a lot of damage. 

As the Forster Collection has been in Oxford since 1776, and the Banks collection was at Christchurch even before that, the Cook-voyage collections potentially span virtually the whole history of pesticide use in museums.  Even though we know that chemicals such as arsenic, mercury and DDT, were routinely applied to museum collections, finding evidence of what was actually done is difficult.  

Label from a poncho from the Tahitian Mourner's costume, giving information on the condition of the feather cape.

A label on the Tahitian Mourner's costume, written just before the Ashmolean's ethnographic holdings were transferred to the Pitt Rivers in 1886, records that the cloak was 'now in a very bad condition' and an entry in the Accession Registers goes on to say that this was 'through the moth, and (it) has been removed to the Museum in the Parks (Oxford University Natural History Museum) and placed under the charge of Professor Moseley to be fumigated.'  We don't know, however, what fumigation involved. 

Sometimes, the Pitt Rivers annual reports give us more of a clue.  In 1946-47, the Curator, T.K. Penniman, wrote that 'we have tried the Clymax spray on all of our material, and have found it thoroughly effective in destroying every sort of pest that attacks every sort of material that human beings use.'  Powerful stuff indeed!  There is also a mention of a fumigation chamber being built so that methyl bromide gas could be used to kill pest infestations on museum objects, but it is not clear whether this was ever actually used.  

Jeremy Uden and Kloe Rumsey, conservation intern, taking samples of surface deposits from a Tongan mat.
The analysis of pesticide residues is being done for us by Andrew Charlton, an analytical chemist at the Wildlife Incident Unit, part of the Food and Environment Research Agency.  He usually works on investigating pesticide uptake by wildlife, especially honey bees.  The samples he works on are usually destroyed during the analysis - not something that is practical for museum objects.  We are using cotton wool swabs dampened with distilled water to take samples of the surface dirt and residues from objects - we know that the object is not damaged in the process, which is of paramount importance, but we have to accept that we may not be able to get large amounts of any residues remaining on the surface onto the swabs. 

Once Andrew receives the swabs, any residues on them are extracted with an organic solvent for analysis using gas chromatography - mass spectrometry (GC-MS), a highly sensitive technique which can detect parts per billion (ppb) levels of target pesticides.  Each target pesticide is detected in the mass spectrometer by the presence of characteristic molecular fragments providing a unique ‘fingerprint’.  To detect the presence of arsenic or mercury compounds, swabs are extracted with dilute acid for elemental analysis by inductively coupled plasma - mass spectrometry (ICP-MS).  Argon plasma at a very high temperature (approximately 6000 to 10000°C) is used to turn the sample solution into ionised atoms (ions). Each element produces ions with a characteristic mass and charge, which are detected by the mass spectrometer. ICP-MS can detect residues of arsenic or mercury pesticides in the swabs at ppb levels.

Cotton wool swabs used to remove surface deposits from a fragment of feather from the Tahitian Mourner's costume cloak.

The results of the analysis will help us to understand how pesticides were used in the museum, and may help answer questions we are starting to ask about whether the pesticides have contributed to damage, such as staining and deterioration in certain areas of some of the objects.  The results will also help us to make sure that the precautions we routinely take when we handle objects, such as wearing gloves and lab coats, are effective.