Thursday, 5 September 2013

'A Black Piece' revisited

This post was written by Emma Schmitt from the Textile Conservation MPhil at the University of Glasgow, who is the summer conservation intern on the Conserving 'Curiosities' project.

Barkcloth 1886.1.1256

'Upon arriving at the Pitt Rivers Museum I was shown the bark cloth object on which it was assumed I would spend most of my time.  The “black piece", as it was listed in Forsters Catalogue, is an interesting and singular object in many ways.  The cloth itself is constructed of three layers, two of plain white bark cloth and one of a decorated black cloth.  The decoration, similar to that seen on the headdress of the Pitt River's second Tahitian mourner’s costume, is itself, rare in form.

1886.1.1637 .9 Headdress, Tahitian mourner's costume

Detail of barkcloth on headdress

At first glace this object is a bit scary, as you can see there are many areas of loss, but on top of that the black cloth appears to be flaking apart in some areas and powdering in others.  The painted areas easily lift up from the surface of the black bark cloth taking both the paint as well as bark fiber with it.  Every time the piece moves other small fragments are lost.

Detail of 1886.1.1256 showing surface damage

The construction of the object has had an effect on some of the damage.  The layers of this cloth have been lightly pasted together.  The black bark cloth has been pasted down in a rather haphazard manner causing creases and folds to form.  These folds can be seen in the photo and, in some places, correspond to the areas where the piece has been damaged. 

Black dyed fibers overall are susceptible to damage for one main reason.  Black dyes tend to be very high in tannin and iron and thus very acidic.  In an acidic environment the fibers can break down at the molecular level eventually leading to visible damage, like we see on this object.  For the most part black dyes in the South Pacific were made using extracts of bark, high in tannin, followed by immersion in mud that would have been high in iron.  Earlier research on this cloth shows that the black portion of the cloth is high in iron, explaining why the barkcloth was breaking down. 

1886.1.1256 - detail of surface under microscope x24

On initial examination of the painted decoration it looked as if white paint had been applied to the black cloth. However, under magnification, the paint appears to have originally been black and, for an unknown reason, appears to have bloomed with a whitish powdery substance.  The question was raised as to whether or not the paint might be a Western paint, brought on Captain Cook’s earlier voyage.  Without chemical analysis of this paint this question is difficult to answer.  The fact that the paint may be black, instead of white, means that it could easily be a local resin.  This still leaves the possibility of it being a Western paint open to speculation. 

While the investigation into the piece leaves numerous questions unanswered it posed a number of conservation issues which led to some interesting experimentation. 

As mentioned, this bark cloth is in poor condition, however it is a rare piece and thus incredibly important to the Pitt Rivers collection.  When we started to discuss possible treatments consolidation of the surface was discussed, to prevent the continuing loss of the back fiber.  Consolidation is the process by which an adhesive is applied to a surface to bind a material together to prevent further loss.  In many cases this is something down to more rigid objects like flaking or powdery painted surfaces.  In dealing with bark cloth the flexibility of the cloth is important and maintaining that flexibility is key to the treatment. 

Research into different methods of consolidation led to the work of Rangi Te Kanawa, a Maori Conservator based at The Museum of New Zealand Te Papa Tongarewa.   Ms. Te Kanawa’s work focuses on the conservation of Mari Cloaks.  Her recent research has lead to the use of sodium alginate, a seaweed based gel, as a consolidate for black dyed New Zealand flax.  Her research showed that, not only did the sodium alginate bind the deteriorating fibers together, but it also had the added benefit of neutralizing some of the acids that are the result of the mud-based dye process. 

Sodium alginate has not been applied to bark cloth by Ms. Te Kanawa so it was unknown how it would affect a very different material.  We set up an experiment to see whether or not the treatment would have a beneficial effect.  Solutions of sodium alginate were made up in various concentrations.  Using fragments of bark cloth from a store of unaccessioned samples we applied the solutions to a dry bark cloth fragment with a brush and allowed them to dry.  The result of the treatment was a metallic sheen on the surface of the bark cloth samples, reminiscent of mica, and a slight stiffening of the material.  Checking of the pH of the samples before and after treatment showed that there had been no change in the acidity of the cloth. 

Unaccessioned fragments of deteriorated barkcloth consolidated with sodium alginate solutions of varying concentrations

A second test was run to see if wetting the cloth through humidification could reduce the metallic sheen.  It was hoped that by wetting the cloth first, the sodium alginate would be drawn into the bark cloth, thus leaving less on the surface.  This treatment was successful in reducing the sheen, however, a test of the pH showed that there was still no change in the acid levels and the fabric still retained the slight stiffening see in the original tests.

Overall the experiment showed that this type of treatment may not be appropriate for bark cloth.  This may be because of the structure of the fabric as the beaten fibers lack the directionality seen in woven fabrics and thus move differently.  The lack of affect it had on the acidic pH as well as the metallic sheen and change in handle made the treatment less than ideal for “the black piece” collected by the Forsters.  An object of such importance and rarity should be treated in a way that is safe and will not visually change the object.   In the end, ‘the black piece’ had a custom-padded board and box constructed for it that will allow it to lay flat and be stored safely, in hope that in the future a treatment may be able to stabilize it and preserve it for future generations.'