Why might scientific testing fail to expose a skillfully made historical forgery?

In the field of diplomatics, scientific testing may fail to expose a forgery if the forger is a contemporary of the intended victim. Because the forger lives in the same age, they have access to the same materials—such as authentic parchment, paper, and ink—that would be expected of a genuine document from that period.1

When a forger successfully secures these appropriate, period-accurate materials, scientific analysis of the physical medium cannot demonstrate that the document is spurious. In such cases, the document cannot be debunked by proving the materials are anachronistic. Consequently, experts must rely on the methods of diplomatics and paleography to examine internal features, such as the writing style, terminology, and formulas, or employ textual criticism to identify anachronisms or conflicts with known historical authorities.1