FADING OF ARTISTS COLORANTS BY A MIXTURE OF PHOTOCHEMICAL OXIDANTS

Thirty-five artists' colorants were exposed for 12 weeks, in the dark, to a mixture of photochemical oxidants including ozone (200 ppb), nitrogen dioxide (75 ppb) and peroxyacetyl nitrate (PAN, 15 ppb) at ambient temperature and humidity. Color changes were measured weekly using a reflectance color analyser and were also calculated from the 380-700 nm reflectance spectra of unexposed and oxidant-exposed colorant samples. Exposure to the oxidant mixture resulted in substantial fading for nine colorants (10-60 DELTAE units) and moderate fading for three colorants (2-5 DELTAE units). Increasing the air humidity from 46 to 83% resulted in a substantial increase in fading. The results are discussed in terms of oxidant-fugitiveness vs colorant chemical functionality and for their implications with respect to oxidant damage to colorants in museums.