It can take anything from an hour to a year for Dr Elize Maza to discover whether a painting is a fake or not. The art authenticator is asked by clients around the world to find out if their Picasso, Warhol, Matisse or Goya paintings are true originals.
Sometimes it will be immediately clear from looking at a client's painting whether it is a fake; but if not Maza will shine UV light on to the work, take a photo of it with an infrared camera or even X-ray it to see what lies beneath its surface.
In one case involving a so-called Goya, the scan showed an entirely different painting by a lesser-known artist underneath.
As well as using scientific clues to put the puzzle pieces together, the "art detective" travels to museums across Europe to find historical examples of the paintings in question. She will also check to see whether an artist's distinctive colour palette or brush strokes have been used.
"There's this whole investigative aspect to my work," she says. "It's really fun."
Picasso is the most forged artist she encounters because of his "prolific output" and the high value of his works. She has yet to discover an original by the Spanish artist. But her most exciting find to date has been an original Andy Warhol drawing.
"Once you do actually find a real work, it's pretty amazing to think that you were handling it and got to play around with it," she says.
But she doesn't always find such satisfying discoveries, and it can be hard to let clients down. "You feel as if you're breaking somebody's dream, especially when they really believe that they had uncovered a treasure."
As for people who say "I could have done that" when they see contemporary art, Maza says it's not that simple: "There are a lot of different factors involved in one single painting. Once you try to mimic a work, you realise how difficult it is."