More from Elyse about how to spot a forgery.
How do you tell if the priceless document you have is the real deal and not a clever forgery?
Investigators first take a historical approach - does the document have a date?
If not, are the paper and method of printing consistent with the era?
A lot of fakes are discovered because they use modern material and their content is inaccurate.
For example, if you have a letter from 1785 that refers to President Washington, you've got a problem since he wasn't elected until 1789.
A detailed scientific analysis of the paper can tell you a lot.
Investigators use spectroscopes, chemical processes and other tricks of the trade to find out about the age, condition and origin of the paper itself.
If your supposedly World War One-era letter has synthetic fiber in the paper, it's a phony.
Synthetic paper wasn't made before 1950.
Finally, stylistic analysis is crucial when authenticating a document.
Penmanship, vocabulary, and phrasing of the words and the form of address can help illuminate the story of the document.
Handwriting experts look for things like the slant of the letter, the crush of the pen on the page and the quality of the line.
For instance, beware of any allegedly Shakespearean document where the Elizabethan letter 's' doesn't look like a cursive 'f.'
Unfortunately, authenticating documents can only take you so far.
No technique exists that can verify which of the five drafts of the Gettysburg address is the one Lincoln read from.
To know that, you'd have to be psychic.