Thursday, January 20, 2011

How Light and Light It Grows

From the desk of Colleen Wilson,
Conservator at the Royal BC Museum

Now that we are past the winter solstice, the days are getting longer and the light is getting brighter. Great! Unless you are concerned about the longevity of material culture, increasing illumination feels wonderful. For those concerned with preserving the physical evidence of the past, however, increasing light levels is bad news indeed.

The colours are much more vivid on the back of this Chilkat blanket.

Energy from the sun, captured, filtered or stored, enables life on earth to go on, but “going on” is just what preservation isn’t. When we conserve something we want it to stay the same, exactly the same; we want it to keep its colour and shape and chemistry intact. But in an organic system, change is not an option. Radiation from the sun provides the energy for materials to combine and the energy for materials to break apart. The energy in light causes the natural colours of fur, feathers, wood and basketry materials to fade; it breaks down the delicate proteins of silk and the gelatin of photographs; it causes paper to turn brittle, rubber to crack, skin to split. Dyed textiles, colour photographs, painted surfaces all lose the vivacity we prize.

And some light is more energetic than others. Ultraviolet radiation is a part of sunlight and of the spectrum produced by some artificial light sources. It is not visible to the human eye, but its high energy is particularly damaging. UV causes skin to suffer from sunburn and worse; artifacts exposed to direct sunlight or unshielded fluorescent light will not last long.

This is not a display of albino birds; they were much more colourful
before lengthy exposure in a sunlit case.

The effects of light exposure are cumulative. Brighter light or longer exposure means greater damage and the effects are irreversible. Like Humpty Dumpty once fallen, no number of horses or men can re-instate colour to a faded dye.

Displaying light sensitive materials is a balance between having enough light to appreciate them while exposing them to the least potential for damage. This is why there are no windows in the Museum’s galleries; sunlight is too dangerous. The glass walls of the entrance and any fluorescent tubes are coated to filter out ultraviolet radiation. Even so, you will not be greeted in the foyer by displays of weaving, butterflies or watercolours. As you move through the galleries, your eyes accustom themselves to less light. An internationally recognized standard for the illumination of sensitive materials, 50 lux, is not very bright, but once your vision is acclimatized it is easier to see fine details.

Most of the Museum’s collection is not on permanent display, however. To many this seems a waste – why keep things that you can’t see? But if we are to pass on the treasures of the past having preserved them for more than our immediate enjoyment, we must keep them safe from the most potent initiator of change. Light is necessary for viewing, but our heritage is safest wrapped in a protective layer of darkness.

Over-exposure to light has caused the dye to fade – the original colour can be seen
where the buttons shielded the fabric around the buttonholes.
On the exposed side of the cuffs, the silk and cotton blend fabric is now
in shreds as light has destroyed the silk.

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The Royal BC Museum is located in Victoria, British Columbia on Canada's west coast. We preserve BC's human and natural history and share it with the world. How do we do that? That's what this blog is about.

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