Is it possible to verify that a signature was made prior to the content of the document it is found on?

Question

In What to do after I signed a blank sheet of paper given to me by my manager?, a distressed individual (B) has signed a blank piece of paper and given it to an adversary (A).

A has openly stated to B that her intention is to use this paper to create a forgery, making it look like the contents have been signed in a normal fashion by B.

Imagine the worst case scenario where A does make the forgery, nobody believes B, and the case ends up in court. Using current forensic methods, could one prove that the contents of the letter were written to it later than the signature?

I know that one can date the age of various items, however, I am unsure if such methods are precise enough to be reliable here.

Does it matter if:

1. A writes the letter five minutes, one day, one month or one year after the signature was made?
2. The text on the document is written by laser printer, ink printer, typewriter, ballpoint pen, other pen, et cetera?

Answer 1

The answer to your question is yes, it is possible with inks to determine how long they have been set and perform a differential analysis to see how far apart the different inks were set. This may not be possible with all ink types, and the closer the attacker sets the ink after the initial signing will play a major factor. Another major factor will be the amount of time between the initial signing and the actual analysis.

The best case scenario for the attacker would be getting the signature, applying their forgery immediately, and then revealing as little about the document as possible. The longer they can retain the document and prevent the analysis, the better off they are. The inverse would be true for an analyst.