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), nit rogen dioxide (75 ppb) and peroxyacetyl nitrate (PAN, 15 ppb) at ambie nt 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 samp les. Exposure to the oxidant mixture resulted in substantial fading fo r nine colorants (10-60 DELTAE units) and moderate fading for three co lorants (2-5 DELTAE units). Increasing the air humidity from 46 to 83% resulted in a substantial increase in fading. The results are discuss ed in terms of oxidant-fugitiveness vs colorant chemical functionality and for their implications with respect to oxidant damage to colorant s in museums.