Light monitoring (or measuring the bear’s forehead)

A large part of our work here at the Castle is monitoring the environment to keep those factors which can damage the collection within certain, less harmful, parameters. There are several environmental factors which are monitored at least daily, if not constantly; Temperature, Relative Humidity and Light.

We record the lights levels in the castle twice daily. Ultra Violet levels in certain areas are also monitored constantly on our automated system and the records stored on the office computer with the temperature and relative humidity, which is recorded by the same system. Ultra Violet cancelling film has been installed on all the windows in the property and cuts out most of the UV, making a vast difference to the light levels in the castle. Other than the morning clean the light readings are the only regular part of routine done daily. Afternoons are used to complete conservation tasks, do admin, research, or work on our interpretation projects.

I really enjoy reading the light levels, especially in the afternoons. I am very interested in the environmental monitoring side of conservation. It is especially rewarding in the afternoons as the castle is open and it gives us an opportunity to interact with the public, which I very much enjoy!

There are set points in all the rooms in the castle that have natural light entering them. Often these points are not on the visitor route, they are located behind the ropes. One of the points is on the forehead of our taxidermy bear, Balu, which amused my mother, hence the title. This results in a lot of curious looks about what I am doing and hopefully curious questions too. I really enjoy explaining to the public what I am doing, especially as it helps make them aware how much work the House team do in order to care for the castle. When I say we do this twice daily people often can not believe it. Doing the readings and conservation work in front of the public helps show them how much work it is looking after the physical history of the country and hopefully inspire them to support us, or keep supporting us.

The effects of light damage on wallpaper

I was privileged enough to shadow the regional conservator when she came to Powis for the annual review of the light levels and this gave me a good understanding to how they are worked out, and why they are set as they are. We have an annual budget, worked out by taking into consideration how often we are open, how long our days are, what objects we have in the rooms, and their vulnerability to light and location with regards to the window. The light levels are set from readings taken with blue wool dosimeters. These dosimeters are left in vulnerable positions in Trust houses and degrade at a known rate. They are set out for 12 months and then sent to a lab for analysis. From this we can tell how much light is affecting that point in the room and work out a safe light level which will hopefully preserve the objects in that area well into the future.

Light is very damaging to objects, and when it fades them it is also damaging them structurally. It damages textiles most quickly but will damage most objects given time, fading dark wood but also lightening dark woods. Something I have learnt is that oil paintings are surprisingly more resilient to light damage than I would have thought. Some of the curtains at the castle are fraying on the edges most often in the light, and the curtains in the Oak Drawing Room have been sent away for conservation to repair the effects of the damage done by the light. These are the most obvious effects of light damage at the Castle.

The annual light allowance establish by the information from the dosimeters and other factors mentioned above is divided up by the number of days the property is open, giving us a daily budget. This daily budget is printed onto our record sheet, which has room to record AM and PM readings for each location. When we go on our rounds, once while opening up and once after we come back from lunch, we adjust the blinds to get the light reading below our set points.

The Megatron

We used to record the light levels using a device called a Meagtron (unfortunately it does not transform into a robot, it just measure light levels). Now however we have a ne Elsec that can not only record Lux but also Ultra Violet, Relative Humidity and Temperature. This new bit of tech’ is very handy for spot reading of the other factors, rather than having to take two different implements round with us. When we were doing the two-week spot check of temperature and relative humidity to check our automated system was calibrated correctly I could have done with another pair of hands for the clipboard and the two different instruments!

The Elsec

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