Removing Foxing Stains from old paper at 157nm

摘要

Using a molecular fluorine laser at 157nm foxing stains were removed successfully from a 16th century old paper. Laser cleaning of stains and foxing from old paper manuscripts is far more effective at 157nm in comparison to different wavelengths without any yellowish after-effect on the paper. This is because at 157nm illumination of old paper, complete bond breaking of all the organic molecules of the paper is taking place. Mass spectroscopy at 157nm and for moderate laser intensities up to 1 mJ/cm~2 of old paper suffering from foxing and including remains of sticky - tape and stains, indicate organic matter disintegration to small photofragments atomic, diatomic or triatomic, which are flying apart with supersonic speed. This is because the dissociative excited states of the small organic radicals, occupy the energy region above 6.5 eV (200nm).