Paintings are often a composed of materials that have been applied and coexist in a series of layers. The commonly identified factors which can lead to the damage of paintings can be separated into those which are inherent, environmental or a physical.
Certain painting materials or combinations of materials are known to have an inherent instability. In some case where a trigger to the deterioration process is known, it is possible to prevent future damage through preventative techniques. However, in some cases the damage could have already occurred, even in the artist’s own lifetime.
Light, heat, moisture, biodegradation and insects all have the potential to cause lasting damage to a painting. Sustained exposure to ultra violet light can lead to the degradation of natural resin varnishes and discolouration of certain pigments, whilst elevated light levels can cause permanent fading. Therefore gallery lighting is filtered and measured, and direct sunlight on the paintings is also blocked.
Excess dryness can be just as injurious as excessive dampness. Fluctuating changes between the two can lead to cycles of contraction and expansion that can cause premature ageing and degradation. Gallery environments are therefore monitored and measures are taken to keep temperature and relative humidity stable. The glazing and backing of frames is also employed to level out these conditions further for individual paintings. Once established within the various layers of painting, mould can prove both damaging and difficult to remove. For this reason localised damp conditions with little airflow are avoided.
Insects can cause damage across the whole collection, but wood-boring insects are particularly harmful to wooden elements within paintings. Vigilance for the warning signs of frass, together with immediate isolation and treatment of any suspected outbreaks, are key to limiting the extent of any damage.
Physical interventions can also harm paintings. Accidental knocks, dents, rips and splashes often require urgent treatment. Physical damage can also be intentional, such as historic treatments or vandalism. Measures are taken to ensure the safe display, handling and movement of the paintings within the museum.