Edinburgh Napier University

  Despite best efforts to remove damaging UV and short wavelength light from museum displays, dyes on historical textiles can still fade or change colour if visible light causes chromophoric compounds to form or degrade. For known light-sensitive dyes, better understanding of the impact of visible wavelengths on them could lead to innovative tuneable LED lighting that offers protection by removing the more damaging wavelengths without perceived colour change to the exhibit or light source.
Published studies about museum lighting mainly concern aesthetic impact on artworks1 with very few reporting chemical changes2. Textile dyes specifically remain un-investigated, so the Filtered Light Project pilot study was initiated to assess visible light effects on major chemical components of the light-sensitive historical dyes safflower, turmeric and basic magenta (fuchsine).
Silk fabrics direct-dyed with carthamin, curcumin and fuchsine were exposed for up to 672hrs to a xenon arc lamp (1.1 Wm-2 @ 420nm) in a QSun XE1 accelerated light chamber at 26±1oC. The lamp light passed through a daylight-through-glass filter3 and then an array of 10nm and 60nm bandpass filters, from 395nm to 755nm and 470nm to 780nm respectively, over the silks. Colour changes to exposed dyed areas were tracked by fibre optic reflectance spectroscopy and exposed dyed areas were sampled regularly for analysis by ultra-high performance liquid chromatography with photodiode array detection3 to detect and monitor chemical markers of change4.
Initial results reveal new compounds in samples filtered at and near visible wavelength maxima for their dye chromophores: curcumin ~400mm (faded after 48hrs exposure), carthamin ~510nm (yellowed after 120hrs) and pararosaniline ~560nm (bluer after 168hrs). This novel study of the chemical impact of visible light on photosensitive dyes therefore suggests that tuneable LED museum lighting for textiles could be protective and so will be studied further in the Filtered Light Project.