Light is one of the most damaging factors in conservation. Light damage is quite easy to spot as causes quite dramatic fading or bleaching but for other objects it can be even more damaging. For textiles like cushions and wall hangings light causes fibers to break down and eventually tear. For organic materials, like paper and animal based glues, they become brittle whilst vanishes and oils harden and flake.
Light falls across a spectrum and different ends cause different problems, such as Ultra Violet (UV), visible (which is the only part of the light spectrum that humans can see) and infrared radiation (which we feel as heat). The most damaging part of the light spectrum for historic collections is UV.
Ideally UV levels should be at zero but it is impossible to prevent UV from reaching collections as it is present in both natural light and light bulbs. Fortunately the light bulbs here in the house do not emit too much UV but the windows and doors present another problem.
In order to prevent as much damage as we can, we follow a strict light plan by limiting the number of hours the blinds and shutters are open. we also use UV filters on all of the windows and doors.
UV filters are made up of a polyester film that absorbs and reflect UV. However it is not perfect and does let in some UV. UV film lasts between 10 – 12 years during which point air bubbles and cracks start to appear. We have recently had our filters replaced which was very interesting to watch.
Firstly the old film had to be removed which is rather simple – it is literally pulled off the windows and then any residue left on the glass is scraped off with a razor blade. The glass is then washed. The new film is then stuck on using water as its adhesive. it sounds very simple but the new film has to be tested before being applied to ensure it is up to the job and then it has to be cut to fit the pane of glass exactly. You can imagine in certain places here, like the windows on the Half landing, taking a long time!