Leo Stevenson, 38, has emulated artists from Vermeer to Monet and Magritte. He is also expert in the processes used to create a false provenance for a work and the materials that would render the final product convincing.
According to Stevenson, painters have become less technically challenging with time: The Impressionists are in turn easier than the Old Masters, while contemporary art is the most easy to imitate, although they still demand a degree of skill.
Even Ben Nicholson, who is more "painterly" than most, would not be relatively unchallenging. "He's more old fashioned than many, and you'd need to know more about tone and colour and paint. But it would be like falling off a log compared to one of the Dutch masters," Stevenson said.
He added: "But a work of art is only as good as its provenance, so a forger's main task is always the creation of relevant documents. This is often far harder to do convincingly than the creation of the artwork. With modern artists, the amount of information you need is relatively small."
Stevenson protects his own works from being mistaken for the genuine article with invisible sign-offs that would be picked up by X-ray. His latest work, a copy of The Concert by Vermeer, which took him 700 hours to paint, includes the words "Elvis Lives" underneath the lute.
But he is aware of exactly how the unscrupulous would create a painting from nothing to sell as an authentic work.
The first objective is to find a canvas from the right period through trawling auction houses, stripping it of paint, while it still has the correct marks on the back.
The forger would then choose a subject that the original artist had either used in a series of paintings, like Monet who painted endless versions of the same thing, or they would focus on a gap in the artist's life. The Vermeer forgeries of the 1940s, for example, were based on the most obscure part of his career.
Stevenson said: "Unless you are a genius, you are never going to get into the soul of the person. But if the artist did a whole series of something, it's not hard to slip an extra one in. Or if it's something the artist was known to have done, without much detail, the bait is already on the hook."
Once the copy or pastiche has been finished, the question is how much scrutiny it will stand. While Old Masters can be tested for chemical changes in the paint, using X-ray and gas layer chromatography, the more recent works are still too young.
A number of paintings that are more than 100 years old and were presented as the works of masters have been revealed using fluorescence X-ray to be the work of minor painters. While the paintings were clearly old the signatures glowed luminously, revealing they were additions.
Among the other additions Stevenson has made to his own pastiches include the words "Benetton" on the cloak of a figure in a work that might be mistaken for a Franz Hals, and his copy of Canaletto's Venetian Lagoon conceals a submarine lurking beneath the first layer of paint.
Stevenson is convinced that until the art market is prepared to wake up to the possibility of forgeries, it will remain a relatively easy art for those who practise it.
"Once something is in writing, in the catalogue or the archive, it is phenomenal the ease with which people will accept it is genuine. It's a bit like telling people not to believe everything they read in the newspapers, only ten times worse. They can be so gullible," he said.
"But for those of us who practise copying and pastiche honestly, it is no different to a classical musician who plays someone else's music and who can get a great deal of pleasure from that. It's half-way between academia and pure artistry - and it is honest."
From the Old Masters to contemporary art - the copyists' guide to the gallery
Jackson Pollock (pastiche only)
Andy Warhol's Marilyn Diptych Copyright: ARS, NY. DACS, London 1996
Van Dyck's portrait of Thomas Wentworth
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