THE CONSERVATION OF BARK ARTEFACTS

Andrea Linckh
(Fachhochschule Köln, Fachbereich Restaurierung/Konservierung)

The aim of my Diplomarbeit as part of the requirements for a Master's degree in conservation techniques at Cologne Polytechnic is to examine methods of preserving an Aboriginal nark basket. The basket is in the collection of the Rautenstrauch-Joest Museum (Cologne): it originates from Melville Island (northern Australia) and was made from bark by an unknown Tiwi Aboriginal artist. The Tiwi basket suffers from severe tears and some deformation due to considerable changes in humidity.

The problem to be solved in the conservation of bark artefacts differs from one object to the next. The material can be very fibrous or brittle which often results in a deficiency of stability and mechanical elasticity. Bark paintings in particular, following a change in relative humidity, tend to bend into their original cylindrical shape. In the process the stress can cause the bark to tear, and at the same time further deformations of the artifact can occur due to the large forces. These damaged bark paintings are difficult to display without provoking further damage.

The bast fibres (inner bark or phloem) of the eucalypt basket under study have lost some of their former elasticity. Their flexibility has to be increased, employing vapour to reshape the basket and rejoin the sides of the tears. Next, both an appropriate adhesive one that will not affect the water-soluble polychromed surface) and a material to be used as a backing to join the tears had to be found. To this end I carried out a number of tests. I conducted shear tests with samples, glued with different adhesives, to arrive at an adhesive with a cohesion slightly weaker than the cohesion of the bast fibres. In case stress should occur again it is important that any tears form in the joint and not in the bast fibres of the basket. Furthermore, I examined the effect of a high relative humidity (95%) on the polychromed surface (the carbohydrate binder and the earthen pigments) of the test samples with regard to their mechanical properties. Finally, I tested the extension (swelling) of eucalypt bast under 90% relative humidity and possible flaking off of the paint.

Documentation by an anthropologist and ethnographic literature helped me to gain an understanding of how bark baskets were and are manufactured by the Tiwi. I also paid attention to the purpose of use, the meanings given to the baskets and their decoration. This ethnographic information guided my search for a means of preserving the basket and to find appropriate ways for a future conservation.

Unfortunately, in contrast to other fields in the conservation of ethnographic artefacts, little is published on research carried out on the conservation of artefacts made of bark and related vegetable fibres. I would be grateful for literature references on this topic. My address is: Immermannstr, 46, D-50931 Köln 41, Germany.