The Effect of Sunlight and Fluorescent Tube Light on Inks and Papers

Following a case involving claimed sunlight effects on paper and ink, and a document examination conclusion suggesting chemical erasure, paper, and ink from various sources were subjected over various periods of time to radiation from sunlight through a window and to radiation from a room fluorescent tube light. All of the papers tested showed a darkening, and most showed a reduction of UV stimulated blue luminescence (fluorescence) and blue light stimulated red luminescence following exposure to sunlight. All of the inks showed changes in apparent optical absorption of light following exposure to sunlight, with some showing dramatic changes of colour, infrared absorption, and luminescence properties. None of the papers or inks tested showed any detectable change upon exposure to the fluorescent tube light. Document examiners should be aware of environmental effects such as sunlight causing changes in the optical properties of paper and inks which potentially might be misinterpreted as a difference in type of paper or ink, or wrongly ascribed to the effects of chemical erasure.