My research into art forgery has taken another interesting turn.

Apparently, a convincing painting isn't always enough. Sometimes the real masterpiece is the paperwork accompanying it.

Receipts. Letters. Bills of sale. Impressive-looking documents establishing that a painting once belonged to someone important, preferably someone who is no longer around to answer questions.

It's called provenance, and in the art world, it matters enormously.

Here's a rather entertaining discovery from an actual FBI investigation: a forger's elaborate paper trail began to unravel because letters supposedly written decades apart had been typed on the same typewriter.

Another document included a ZIP Code that hadn't been invented when the letter was supposedly written.

Imagine going to all that trouble to manufacture a piece of history, only to be betrayed by the postal service.

I've been spending more time investigating how auction houses and art experts approach questions of authenticity. The deeper I dig, the more fascinating the subject becomes.

After all, a forgery doesn't necessarily have to convince the entire world. Sometimes it only needs one respected person to declare it genuine.

And once that happens, the story can become considerably more valuable than the painting.

I'm beginning to suspect that researching art forgery is rather like opening a locked cabinet in an old house.

You never know what you'll find.

And occasionally, you discover that someone has been lying about what's inside for the better part of a century.