Volume 36, Issue 2 (March 1991)
Detection of Nonvisible Writings by Infrared Luminescence and Ultraviolet Fluorescence
The presence of nonvisible written material was detected on documents during an examination for infrared luminescence. An experiment was conducted to examine absorption by paper of noncolor ink components from documents bearing written material. Various inks were used to prepare sample writings. Each sample writing was prepared on an original sheet of paper with a corresponding undershcet. These sheets were then placed between upper and lower protective sheets. Each four-sheet sample was left intact for a 72-h period. The presence of nonvisible writing resulting from the absorption by paper of noncolor ink components was detected on particular sample sheets when examined for ultraviolet fluorescence and infrared luminescence. The methods used and the results are discussed.