In Nondestructive Ink and Paper Examinations, handwriting expert witness Ronald N. Norris writes:
When most people think of ink analysis they, think that it is a destructive examination which means my document is going to be severely damaged or destroyed. That is not completely accurate. There is a way of examining ink entries without damaging the document, and it is usually the only test necessary to resolve the issue of ink differentiation.
The examination process, known as infrared fluorescence, or luminescence, was developed by Mr. H. Gibson for use in the study of tissue samples. Forensic document examiners have used the same technique for nondestructive ink differentiation examinations for many years. Because a technical discussion of the process is beyond the scope of this paper, the reader is referred to an article on the web at http://msp.rmit.edu.au/Article_02/04.html. At the same web site there are links to other articles about the theory and equipment necessary to perform nondestructive ink examinations.