Wood

Ideal conditions for storing and displaying wooden objects

This section outlines the best long-term storage and display environment for wooden objects. But please note that if an ideal environment cannot be created, the emphasis should be on providing a stable environment.

Ideally, all wooden objects should be stored in an environment where temperature is constant and moderate-in the range of 18–20C. Changing temperatures affect relative humidity levels; so if temperatures are generally outside this range in your area, it is important to try to keep fluctuations to a minimum and to ensure that they are gradual. High temperatures can accelerate degradation reactions, and cause wood to dry out and become brittle.

Relative humidity should be constant and in the range of 50–60%. For composite objects, a compromise may have to be reached between a relative humidity that is ideal for the wooden components and the preferred relative humidity for the other component materials, for example, metals.

Wood swells and shrinks with changes in relative humidity. Wooden objects undergo dimensional changes when the relative humidity changes. This is generally a reversible process; but the speed of the process varies-drying takes longer than moisture absorption.

Avoiding rapid or excessive fluctuations in relative humidity is critical. It is better to leave a wooden object in a non-ideal relative humidity environment to which it has acclimatised than to suddenly change the relative humidity.

If relative humidity changes significantly, then swelling or shrinking can cause irreversible damage to a wooden object—this can include warping, twisting, splitting and cracking. Joints can pull apart, and panels distort. Cleavage and loss of paint can occur on painted, wooden items. This phenomenon is the most common and most preventable cause of damage to wooden objects.

Mould grows where relative humidity is continuously above 65%; but relative humidity levels of 60% and less are not favourable to mould growth.

Items which are at risk of drying out too quickly after they have come from moist conditions should be kept in an environment where the relative humidity is in the range of 50–60%. Items which are acclimatised to drier conditions should be kept in an environment where the relative humidity is in the range of 45–55%.

Light should be kept to the minimum necessary for the activity. Wherever possible, items which are not on display should be stored in the dark. If light is not required for viewing while the works are being stored, then there is no need for them to be illuminated. This reduces the risk of materials fading and becoming discoloured.

The brightness of the light should be below 250 lux.

For objects on display, the maximum exposure to light should be 650 kilolux hours in one year.

Ultraviolet radiation should be eliminated completely, because it causes irreversible changes to the appearance and structure of the wood surface and greatly accelerates degradation reactions. Ideally, the UV content of the light should be less than 30 µw/lm and no greater than 75 µw/lm.

Avoid exposure to the sun if possible. Research shows that after only three days' exposure to the sun, the lignin is completely broken down in the surface of a piece of wood. This affects both the colour and texture, as well as the strength of the wood, often resulting in wood fibres shedding off the surface.

Protect items from dust and pollutants.