ONE of the biggest problems facing wooden artworks is that, over time, they are attacked by pests, thereby destroying the wood’s uniqueness.
Pests can mean big trouble for wooden objects, and these can be from three categories of pests, which are: Microorganisms, such as mould and mildew; insects such as moths, beetles and silver fish, and vertebrates, such as birds and mammals. However, in order not to lose valuable wooden work of arts, the best preservation is a combination of prevention and constant vigilance. Organisms which destroy wood have been found in virtually every environment. Unfortunately, the optimum temperature range of 24°c-32°c is one that humans are comfortable in, so temperature is not a practical way to control the organisms.
There are two main types of wood destroying organisms — fungi and insects, and infestation by either one can lead to complete destruction of a wooden artwork. In fact, infestation by one usually leads to infestation by the other. Fungi, including moulds and mildews, are everywhere in the environment. Fungi are simple plant-like organisms which do not have chlorophyll to provide their own food. In essence, they have a parasitic relationship with their host. They rapidly multiply in a supportive environment and send seed-like spores out (sometimes air-borne) to extend their range.
Some fungi do not affect the strength of wood by their activity, and they may only stain the wood. However, some can completely destroy the wood cellulose and lignin.
Ultimately, the wood residue crumbles to a powder form. There is almost no point trying to eradicate or exclude fungi since they are commonly found everywhere. However, artists can successfully control their consumption of wooden objects, simply put, if the relative humidity is kept moderate (less than 60%), there will be virtually no problem with fungi, but insects, such as beetles in their larval stage, are among the most destructive.
These insects lay eggs in wood, and the maturing larvae eat continuously, only emerging to mate and continue the cycle. The emerging adult will leave a small exit or flight hole about 1.5mm in diameter.
Termites can pose a threat to furniture, but are usually common in the wooden building surrounding collections in the museum. Other insects present a special problem since they may not even use wood for food. Some ants and bees tunnel through wood, creating galleries for shelter. They may not usually pose a problem to furniture, but can be a major destructive agent in historic buildings or monuments.
It follows then that removal of one or more of the favourable growth conditions is sufficient to arrest the spread of biological deterioration. The simplest method to deter fungal and insect damage is to maintain and monitor a moderate environment (that is, a properly-regulated environment), since the most controllable factor is the moisture content, good collection care will include maintenance of a 40 – 60 per cent relative humidity.
Naturally, some special objects may require other conditions, but most will do well in this range. Wood has variable degrees of natural resistance to decay.
Overtime, craftsmen have selected wood for use in adverse environments. Some woods last for years, but others decay in one season. Woods with long resistance can be treated with preservatives. Insects and fungi show little interest in penetrating paints and varnishes to consume wood. So those objects, which are or can be coated, will be better off.
- Alli is of the National Museum of Unity, Ibadan.