Faded book spines, curtain backs, and tapestries; we’ve all witnessed the irreversible damage that light can cause to decorative objects. Such colour change can detrimentally affect the aesthetic appeal, interpretation, and accessibility of a collection. Like other heritage institutions, The National Archives strives to both preserve and provide access to its collections. A balance must be struck between exhibiting, and exposing the collection to potentially damaging light – or not exhibiting and restricting access to the collection. The National Archives’ exhibition lighting policy achieves this balance in most cases, but in others, such as the exhibition of unique and delicate textiles from the Board of Trade Design Registers that are prized for their colourful vibrancy, further analysis was required. In this case we used a technique called microfading to determine if the textiles could safely go on display in The Keeper’s Gallery.
Four brightly coloured printed textiles (BT52/4285/292274, BT52/4079/272017, BT52/5373/372726, and BT52/3037/109909) dating from 1914 to 1937 were proposed for exhibition in The Keeper’s Gallery (Figures 1 and 2). These textiles are just a few of the many fascinating representations of copyrighted designs from The Board of Trade Design Registers. Crucially, the exhibits hadn’t been exposed to much light over their lifetime and as such the colours closely resembled the manufacturers’ original intentions. Preserving these colours was paramount and required selecting appropriate lighting conditions for the exhibition.
Exhibition lighting policy
The National Archives’ exhibition lighting policy details measures to minimise the impact of lighting on an object during exhibition based on the object’s light-sensitivity. An object is given one of four ratings ranging from’ vulnerable’, for objects most at risk of damage through light exposure, to low sensitivity, where there is little risk. Correct categorisation of an object is essential for achieving the optimum balance between access and preservation. Unfortunately for these particular textiles, categorisation was complicated by a lack of information on the light-sensitivity of the colours themselves. Without this evidence the textiles would be displayed based on the sensitivity of the base material they were printed on; in this case, woven textiles of wool, silk, cotton, and linen. This is fine if the colours are equally or less sensitive than the base material. However if the colours are more sensitive than the base material, the textiles could fade due to the light exposure. In order to determine which category the textiles belonged to we needed to find out the light-sensitivity of the colours in the textiles. An impossible task by eye but easily done using microfading.
Microfading involves measuring the colour change of an area that is exposed to a high-power beam of light over a specified period of time (normally 10 minutes or less). We conducted the test at UCL’s Centre for Sustainable Heritage (London) where we filtered the light to remove ultraviolet and infrared to replicate the conditions in The Keeper’s Gallery (Figure 3). Importantly for heritage institutions, such as The National Archives, microfading is a micro-destructive technique. While some fading occurs to the sample during testing it is barely if not invisible to the naked eye, due to the small size of the light beam used (3 µm diameter). Consequently, you can’t see the exposed area on the material once analysis is complete! The measured change in sample colour is only meaningful when compared to the ISO/Blue Wool Standards using the same experimental conditions. These standards are widely used in the heritage sector and form the basis of the light-sensitivity categories in the exhibition lighting policy.
Through microfading the textiles we identified that two of the four textiles were categorised ‘vulnerable’ due to the light-sensitivity of the colours in the designs.
Exhibition lighting conditions
In view of the results we decided that the textiles could be exhibited using the recommendations for ‘vulnerable’ materials i.e. that they can be exposed to light for up to 20,000 hours within a 5 year period. This equates to the planned 11 weeks of display in The Keeper’s Gallery that ends on the 18th May 2014 (Figure 4). During this time the colours of the textiles will be monitored using colorimetry to ensure that no perceptible colour change occurs during the exhibition.
Microfading was vital in helping us to establish the correct lighting conditions for these rare and beautiful textiles, without compromising their preservation or unnecessarily limiting access.