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Conserving the Lewis Chessmen
All the Lewis chessmen have recently been examined by British Museum conservators to investigate their condition and carry out any treatment required for them to be safely displayed.
Some of them have undergone minor conservation treatments over the years since their discovery to stabilise them but on the whole are in relatively good condition. In some cases these old coatings and adhesives had changed with time and become more noticeable or had degraded leaving unsightly remains visible on the surface.
Ultraviolet light was used to reveal further evidence of old treatments not visible in normal light. The materials used in these previous treatments have been characterised and documented, and provide an insight into changing approaches to the selection of conservation materials over the last century.
Walrus ivory has a distinctive structure with two distinct inner layers of dentine, which affects the way in which it deteriorates and this in turn affects the approach to its conservation. In a few cases there was evidence of old movement such as cracks and breaks between the primary and secondary dentine.
Light cleaning and some stabilisation was needed. Splits and cracks were treated with a dilute adhesive and areas of loss filled. Only adhesives and fill materials stable, reversible and also flexible enough to accommodate slight size changes in the ivory, were used.
As a very sensitive material, prolonged exposure to water can leave ivory brittle and chalky, while acids readily attack it. It also reacts to changes in the moisture content of the air. If the humidity in the environment drops, the ivory loses moisture and contracts. If the humidity increases, it absorbs moisture and expands. Fluctuations in humidity (or exposure to heat) can cause ivory to crack, split or warp, so the chessmen are kept in a stable environment of about 40-55% Relative Humidity and at a temperature of 16-20 ºC.
It is likely that some of the chessmen were once coloured although analysis has not been able to detect any colouring agents still present. Nevertheless, since some colourants are light sensitive, the lighting within the display-case is kept at a low level, so any remaining colour will be preserved.