The recent discovery of an art forger's workshop reminds us of the long history of fraudulent artworks – here are the simple rules to work them out.

It's everywhere: fake news, deep fakes, identity fraud. So ensnared are we in a culture of digitised deceptions, a phenomenon increasingly augmented by artificial intelligence, it would be easy to think that deceit itself is a high-tech invention of the cyber age. Recent revelations however – from the discovery of an elaborate, if decidedly low-tech, art forger's workshop in Rome to the sensational allegation that a cherished Baroque masterpiece in London's National Gallery is a crude simulacrum of a lost original – remind us that duplicity in the world of art has a long and storied history, one written not in binary ones and zeroes, but in impossible pigments, clumsy brushstrokes and suspicious signatures. When it comes to falsification and phoniness, there is indeed no new thing under the Sun.

On 19 February, Italy's Carabinieri Command for the Protection of Cultural Heritage uncovered a covert forgery operation in a northern district of Rome. Authorities confiscated more than 70 fraudulent artworks falsely attributed to notable artists from Pissarro to Picasso, Rembrandt to Dora Maar, along with materials used to mimic vintage canvases, artist signatures, and the stamps of galleries no longer in operation. The suspect, who has yet to be apprehended, is thought to have used online platforms such as Catawiki and eBay to hawk their phoney wares, deceiving potential buyers with convincing certificates of authenticity that they likewise contrived.

News of the clandestine lab's discovery was quickly followed by publicity for a new book, due for release this week, alleging that one of The National Gallery's highlights is not at all what it seems. According to artist and historian Euphrosyne Doxiadis, author of NG6461: The Fake National Gallery Rubens, the painting Samson and Delilah – a large oil-on-wood attributed to the 17th Century Flemish master Peter Paul Rubens and purchased by the London museum in 1980 for £2.5m (then the second-highest price ever paid for a painting at auction) – is three centuries younger than the date of 1609-10 that sits beside it on the gallery wall and is incalculably less accomplished than the museum believes.

Doxiadis's conclusion corroborates one reached in 2021 by the Swiss company, Art Recognition, which determined, through the use of AI, that there was a 91% probability that Samson and Delilah is the work of someone other than Rubens. Her assertion that the brushwork we see in the painting is crass and wholly inconsistent with the fluid flow of the Flemish master's hand is strongly contested by The National Gallery, which stands by its attribution. "Samson and Delilah has long been accepted by leading Rubens scholars as a masterpiece by Peter Paul Rubens", it said in a statement given to the BBC. "Painted on wood panel in oil shortly after his return to Antwerp in 1608 and demonstrating all that the artist had learned in Italy, it is a work of the highest aesthetic quality. A technical examination of the picture was presented in an article in The National Gallery's Technical Bulletin in 1983. The findings remain valid."

The divergence of opinion between the museum's experts and those who doubt the work's authenticity opens a curious space in which to reflect on intriguing questions of artistic value and merit. Is there ever legitimacy in forgery? Can fakes be masterpieces? As more sophisticated tools of analysis are applied to paintings and drawings whose legitimacy has long been in question (including several works attributed to Leonardo da Vinci, such as the hotly disputed chalk and ink drawing La Bella Principessa), as well as those whose validity has never been in doubt, debates about the integrity of cultural icons are only likely to accelerate. What follows are a handful of handy principles to keep in mind when navigating the impending controversies – five simple rules for spotting a fake masterpiece.

To be a successful art forger........

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