In Nondestructive Ink and Paper Examinations, ink differentiation expert witness Ronald N. Norris writes:
The forensic examination of documents involves more than just the identification of handwriting and hand printing. Frequently, questions concerning the differentiation of inks, obliterated writings where it is important to determine what is being covered up by the overwriting, and paper examinations are necessary. To conduct these examinations, special techniques involving light of different wavelengths, cyan/green and ultraviolet, in conjunction with special filters and a digital camera, are frequently employed instead of using destructive techniques. This paper is an attempt to explain how this is accomplished.
In any type of forensic examination of documents, a conservative assessment of the observable evidence present on and in the documents is absolutely essential. The cardinal rule, the evidence in the documents may not provide the basis for a definitive answer in every case or examination. The techniques described in this paper have their limitations. The results must always be reported that include the limitations.