Art thieves have put on display stolen fragments from works by a rollcall of the 20th century's best known artists including Andy Warhol, Jeff Koons and Robert Rauschenberg and even, they say, a tiny chip from something considered by some the century's most influential of all: Marcel Duchamp's Fountain.  Eva and Franco Mattes do not deny their audacious two-year spree from public museums. And they claim to have stolen only tiny shavings or threads or chips of the art. "We did not consider it vandalism at all," said Franco Mattes. "It was pretty easy. And we were 19 years old, we did not think so much of the consequences."  The Matteses said they stole the fragments from 1995 to 1997 and revealed the thefts publicly in 2010. As well as displaying them at a new solo show in London, the couple show a film of their last theft in 1997, in which they steal a fragment of burned cellophane from Alberto Burri's Bianco Plastica, in a gallery in Italy.  The Matteses said they were trying to "revitalise" the works they stole from. "A lot of the works were so crazy, strong and powerful when they were made, like Duchamp's Fountain, but became so accepted and it was like energy had been sucked out of them by being put in a museum. The work maybe dies a little bit.  "We consider what we did a tribute to these artists – it is like a medieval relic, you keep it because you want to protect it and preserve it. We were acting out of faith, not anger."  Some thefts took longer than others, the artists said. For example it took two days to find the right moment to peel the date from Duchamp's 1920 work Fresh Widow. There is also a thread of canvas from Kandinsky's Landscape with Red Spots No 2 (1913), a dot of oil paint from Chagalle's Rain (La Pluie), and the tiny chip from Fountain, the urinal in the Pompidou, Paris, which revolutionised conceptions of what could be art.  The New York-based artists – also known as 0100101110101101.org – are self-confessed thieves, hackers and fraudsters in the positive senses of the words and their works go on display on Friday in their first London show.  Also in the show are works they made while pretending to be someone else, for example a stuffed cat in a cage with a canary on top – which they claimed was by the Italian artist Maurizio Cattelan.  "We did tell him and he sent us an email, basically saying he loved it," said Franco Mattes. "I was scared because I really like and respect his work."  Mattes said they were offered Cattelan-sized money for the work but confessed their duplicity, causing the offer to be dropped by a few zeroes.  The Matteses are considered net art pioneers and they show some disturbing work in the show. For example, in a piece called No Fun, Franco pretends to hang himself in his New York apartment and broadcasts it in a webcam-based chatroom. Side by side are the "suicide" and reactions from other people which dent your faith in human nature.  • Eva and Franco Mattes are at the Carroll/Fletcher gallery in Eastcastle Street, London
Eva and Franco Mattes pilfered shavings, chips and fragments from illustrious works by Duchamp, Burri, Warhol and Koons