All light contributes to the deterioration of archival documents. Light damage is cumulative and irreversible.We require light to see documents however we must be careful to monitor the use and level of light in order to minimize permanent damage to material. Light, by definition, is the band of radiation to which our eye is sensitive. Ultraviolet radiation (UV) and infrared radiation (IR) are not visible. Ultraviolet and infrared are not necessary for seeing (except in rare cases of UV fluorescent colours). The yellowing and disintegration of archival material by UV light is largely due to uncontrolled environmental conditions therefore, careful monitoring is required to avoid damage to documents.
UV light causes yellowing, chalking, weakening, and/or disintegration of material and UV content should be removed, either by choosing low UV or free light sources or by blocking the UV content by the use of light filters.
The only way to assess the level of light and the effectiveness of UV-filtering products is to measure the UV levels emitted using a UV monitor. Correlated Colour Temperature (CCT) measures the quality of light that passes from “cool” to “warm.” The units are degrees Kelvin, abbreviated simply to K. The Kelvin scale is named after the Belfast-born, Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907). A short biography of Lord Kelvin can be found here and a collection of his papers is held at Special Collections
Lina Kinduryte and Rowan Anderson are both students on Club 21 placements at Glasgow University Archive Services. They have been assisting the Preservation Unit here by helping out with the Preservation Assessment Programme Project. Over a period of time the students took visible light measurements in different places in our repositories (archives stores) and also in our searchroom. Each source of light was measured at a 45 degree angle. Lina and Rowan took the UV light measurements in several different locations in the repository and collected data and analysed the results afterwards.
The measurements taken suggest that we need to reduce the light levels in some areas of our repository and that some of the sleeves that cover fluorescent bulbs and control UV light need to be replaced as they have become brittle. Based on the results of the light tests a decision was also made to apply films (containing organic UV-absorbing compounds) to the surface of the windows in our repository to prevent UV light from penetrating through the window and affecting the documents contained within.
Our blog is the best way to say thank you to our volunteer students for the work that they do in the day-to-day care and preservation of our archival material and to welcome them to the world of Preventive Conservation!
Categories: Archive Services (GUAS)