Conserving bark paintings

National Gallery Conservation Department has been actively involved in developing conservation techniques and researching material characteristics of Indigenous bark paintings since 1986. Looking after bark paintings in the collection requires a deep understanding of their raw materials, techniques of production as well their cultural significance. Materials used for creating bark paintings remained mostly unchanged for decades – the earliest surviving examples of bark paintings date from the mid-19th century – and include a sheet of bark, most commonly from stringybark Eucalyptus Tetradonta; naturally occurring, mostly mineral pigments (red, white, black, and yellow); and binders used to adhere the loose pigment particles and apply them as a paint layer. Natural binders include orchid juice or turtle eggs used until 1970’s. Now, these are substituted with readily available, synthetic materials such as PVA [polyvinyl acetate] commonly available in the form of the wood-glue Aquadhere. This substitution brought about an aesthetic change in the appearance of the painted surface — from a relative matte, porous paint made with natural, weak binders, to a shiny, cohesive, dense appearance in more recent paintings. This change in the art practice was brought about by artistic experimentation with readily available materials, and also the interest of collectors in an increased permanence of the paintings.

All conservation treatments and preservation techniques, as practiced by museum and gallery conservators, are constrained by the professional ethic of minimising intervention, maintaining present conditions of the painting. It is accepted by conservators that the original painting should not be compromised by any cosmetic treatments (such as restoration).

Most conservation problems related to the deterioration of bark paintings are a result of the inherent properties of the materials and techniques of their manufacture. For example, the bowing and warping of the bark support comes from the tendency of bark — as a part of a tree trunk — to return to its natural, cylindrical shape. This often stands in conflict with the European idea of a painting, traditionally a flat surface. Generally accepted European frameworks for consideration of works of art are discarded in relation to the distinctive qualities of bark paintings.

The cracking and splitting of the bark — apparent in many paintings — is due to the bark’s natural movement in response to changes in relative humidity. Frequent and rapid fluctuations in moisture levels bring about high stresses in the wood structure which are released by cracking and splitting. There is little that can be done to rectify this problem once it occurs. Preventive steps can be taken which involve maintaining stable environmental conditions during storage and display and minimising the risk of further damage.

Another common problem found in many paintings regardless of their age is the instability of the paint layer, which is evident in the flaking paint and the resulting losses. There are many factors, which influence the long-term stability of the paint layer – these include the inherent properties of pigments used, technique of paint preparation and application and the environmental conditions the painting was subjected during its life. Each painting has its own unique characteristics and needs to be carefully examined by a skilled conservator familiar with the practices of bark painters. There is no easy cure or recipe to rectify the often-serious problem of paint flaking. Fluctuating environmental conditions are a common cause of flaking paint, as the movement of bark responding the relative humidity changes leads to separation of the rigid paint layer from the flexible support.

To stabilise the paint, conservators choose an appropriate agent (consolidant), which is carefully introduced under each flake, adhering the lifting area back to the bark support. This very time-consuming treatment is carried out locally. There is no effective and ethically acceptable preventive treatment which can be applied to a paint layer to prevent damages in the future. Some owners and collectors spray bark paintings with various ‘fixatives’ to ensure the stability of the paint. Such treatments are ineffective. There is insufficient penetration of the ‘fixative’ through the paint layer, which usually sits on the surface. The materials used for such treatment are frequently unstable and in time show signs of ageing, such as yellowing, cracking or lifting. Once applied to the paint, these ‘fixatives’ cannot ever be removed and therefore contribute to the deterioration of the painting and its appearance.

Dirt and dust can exacerbate the difficulty in treating an unstable paint layer. Dust and dirt accumulate on the surface during the life of a painting. This needs to be carefully removed before any consolidation takes place to ensure the dirt is not permanently fixed to the surface. Good preventive or housekeeping measures are essential in caring for bark paintings. They are best stored flat and protected from dust to prevent any loss of paint and dust accumulation on the surface. When exhibiting paintings on bark at the National Gallery, they are not framed but presented as they have been created — without any visual boundaries. They rest on brackets, or shelves and secured to the wall by unobtrusive clips. Deteriorated paintings can be displayed horizontally or at an angle to minimise the risk of any further damage.

Preservating bark paintings is a developing and fascinating field. It requires finding new approaches and solutions to all aspects of their care – often stretching established museum practices in storage, conservation and presentation as objects for display. This gradual process of evolution will bring about a new level of appreciation for Indigenous bark paintings as a distinctive art form, unlike any other in the world.