Studies on the conservation of waterlogged wood in New Zealand

Abstract

This thesis is a study of properties of certain New Zealand woods recovered from waterlogged environments. The woods are those which were commonly used by the pre-european Maori to make artefacts, and the properties are those which affect the way these artefacts can be conserved after they have been removed from wet archaeological sites. The properties studied were (a) the species of wood used (b) the forms and shapes of the timbers (c) the densities (d) directional shrinkages, and (e) directional penetrabilities of each wood. The results of this research are intended to aid conservators to correctly treat the artefacts. The research began with studies of (a) New Zealand wet site archaeology, (b) the structure and properties of wood in general, and (c) the techniques used to conserve waterlogged wood worldwide. This was followed by a survey of circa. 1000 wooden Maori artefacts from Museums involving the identification, by thin section microscopy, of wood species. 30 wood types from 22 tree species were found to have been widely used. A collection was made of samples of each type in different states of decay. Each sample was tested for density, directional shrinkage and directional penetrability. The penetrability was measured by vacuum impregnation of water into wood blocks. Results were compared to those from sound oak (Quercus robur), a wood which has been studied intensively by conservators in Europe. Detailed summaries of the conservation properties of 26 wood types are given. This reveals that while some New Zealand woods are easy to conserve others provide considerable problems. The latter woods are all highly durable in wet sites, extremely dense, have high shrinkages and are highly impenetrable. These will require special types of treatment to avoid damage during conservation.