Paper Fluorescence Check
Detecting modern paper used in historical forgeries.
The Blacklight Test
Starting in the late 1940s and becoming standard by the late 1950s, paper manufacturers began adding Optical Brightening Agents (OBAs) to make paper appear whiter.
If you shine a UV/Blacklight on an allegedly authentic Abraham Lincoln document and it glows a bright, synthetic blue, the paper is modern and the document is a forgery (or a modern reproduction).