Leading conservator George Monger assesses the dangers of light damage to antiques and art, and what you can do to take preventative measures
Out of the Light
In the 1970s, a well-known textile conservator of the day, speaking at a conservation seminar, suggested the best way to preserve textile collections was to keep them in the dark, turning a light on to inspect the collection once a year – and even that was too much. Indeed this was the view of many conservators at this time, which always begged the question – what was the point in preserving the collection?
In 1978, Gary Thompson head of conservation at the National Gallery published his ground-breaking book, The Museum Environment, which set apparent acceptable light levels for displays. However, over the last 40 years the conservation mindset has become more pragmatic, accepting that few institutions and collectors can achieve the environmental conditions of the National Gallery, and that some materials are more resilient to changing environments than others.
The Problem with Light
However, we are faced with an intractable dichotomy: we need light to see the collection or object but, at the same time, light can be damaging to some elements of the object.
What is Light
Light can be thought of as packets of energy travelling at different rates (wavelengths), the particular wavelengths which concern us are those which we identify as visible light and ultra violet (UV) light.
Sunlight is approximately 10 per cent UV light, much of which is filtered by the earth’s atmosphere, and is generally invisible to the human eye. It is often considered the damaging element of light but, it is important to remember, visible light is as damaging as the UV element.
Light damage to Antiques and Art
Obviously, not every material is sensitive to light damage – metals for instance will not necessarily be damaged by light itself (but degradation can be exacerbated by the heat inherent in the light). But we can identify materials and objects most likely to be degraded by visible and UV light.
The types of object which are sensitive to light damage can be divided into two overall groups: the first group includes oil and tempera paintings, plastics, ivories (bone, horn, wood where the surface colour is important) and lacquer. The second group is made up of costume and textiles, watercolours, manuscripts, printed books, printed ephemera, dyed leather and natural history, such as taxidermy.
Recommended Light Levels
For the first set Gary Thompson recommended a maximum visible light level for sensitive materials of 200 lux and for the second set of objects 50 lux, with a maximum UV level of 75 microwatts per lumen (μw/l).
There is no direct relationship between the lux level and the UV content of the light.
However, the effects of light are cumulative, so that 1,000 lux for one hour causes the same level of damage as 100 lux for 10 hours, so we should be considering the light exposure in lux/hours rather than the recommended light levels; this means that the viewing light can be higher than, say, 200 lux, for a short period if the sensitive item is kept shaded or in the dark when not being viewed.
Damaging Effects of Light
The effect of light is insidious and the degradation can be unnoticeable until it has gone too far, such was the case in a recent commission to treat panelling in a boardroom where the eastward facing wall had suffered less light damage than the panelling on the window side.
However, the fading was only noticeable when the pictures and shields on that wall were removed, leaving their darkened images on the wall.
Fortunately, it was possible to repair this damage, but in many instances the damage, which can be fading or colour changes or breakdown of varnishes, is irreversible.
Preventing Light Damage
How, can the damage by light be prevented? The only sure way of preventing light damage is to keep the object in the dark, which is not an option for most.
Consequently, the only practical solution is to minimise and retard degradation by ensuring that general light levels are low.
It is not possible to discern lux and UV levels without specialist equipment, apart from being able to say that the light is bright or dull. If you can gain access to the equipment it is possible to map light levels in a collection storage or display area so that sensitive material can be positioned in the least damaging area.
However, even without the equipment it is possible to develop display and storage strategies to reduce light exposure.
Filter UV Light
Filtering out the UV light is a good start, most incandescent lights emit little or no UV while fluorescent lights are renowned for emitting UV, which is why museums and galleries fit UV filtering sleeves to light tubes (having said that, many contemporary fluorescent tubes emit very low UV levels).
UV filter film can also be fitted to windows, these are not too difficult to apply but are quite time consuming to cut and apply. The film has an added advantage to prevent the complete breakage of the window. It may, however, be impractical to fit filters to windows so the recommendation is to ensure that any items susceptible to light damage should be placed where it does not receive direct sunlight.
Controlling Visible Light
The visible light, too, should also be controlled. For paintings and watercolours, for example, the light levels can be controlled by not having direct light onto the object and ensuring that the object is not directly facing an east or west-facing window.
If the collection is maintained, shown or stored in a specific room, then it may be practical to fit blinds or keep curtains drawn when the room is not in use. This would ensure that the lux/hours are reduced.
If additional lighting is being used, such as LED or fibre optics, using a controllable source to adjust the light’s intensity is recommended.
If we want to see and appreciate objects which we have collected, there is a price to pay in that the light can be damaging over time so that the only thing we, as collectors, or people entrusted with the care of historic objects, can do is retard or minimise this damage, by giving careful consideration about the positioning of the object and the quality and intensity of the lighting being used.
George Monger ACR is a conservation expert and consultant for a number of museums and national heritage organisations. If you have a conservation query for him email: firstname.lastname@example.org or call him on 01449 677900.