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Distinguishing a genuine artwork from a forgery can be worth millions. Art detectives and analyse pigments, fingerprints and DNA to tell you who painted your family heirloom, and when. The art world loves to loathe them, but as the pair explain to Laura Spinney, it can’t live without them. Indeed, with controversy raging over a purported , their skills are more invaluable than ever.

How did you become sleuths?

Peter Paul Biró: I’m an art conservator, and in 1983 a fellow came to me and my brother with a big ugly landscape he wanted restored (see image). When we told him the cost he nearly fainted. He asked a small sum for it instead, and we bought it, intending to use it to show what cleaning can do to an old painting. We soon realised that there was an intact painting underneath, and it was no sloppy amateur job either (see image). We eventually , based on fingerprint and pigment analyses (see image). After that I began researching the use of physical evidence from paintings – DNA and fingerprints.

Nicholas Eastaugh: In the early 1980s I was working in art conservation, but I have a background in physics and I felt frustrated that analytical technology was not being applied to the authentication of art. Scientific departments in museums and galleries tended to concern themselves with conservation and documentation. So I set up , an organisation which researches historical pigments.

What is scientifically novel about what you do?

PPB: The fingerprint and DNA analysis I do has been used to solve crimes for years. The novelty is in the realisation that artists have not only left their art behind, but also marks of themselves, in the form of fingerprints and other contact evidence.

NE: A lot of the techniques I use – X-ray, infrared, chemical analysis of pigments – were established by the 1920s. To apply them to art I realised we needed to develop a more probabilistic approach. That’s what is new. For example, if a pigment was invented in the early 18th century, but didn’t become widely available until the middle of that century, we can use the pigment’s presence or absence in a painting, together with other historical information about it, to calculate the probability that it was painted between those dates. A probability, mind you, not a certainty.

What can you offer by collaborating that you can’t offer separately?

PPB: Corroboration. Converging strands of evidence. Take a case that came to Nicholas some years ago. It was a large painting that looked like a Turner. The pigments checked out, but plenty of other painters used those pigments at the same time, so they didn’t nail Turner. I came to London and found a fingerprint in the painting that matches one in the Turner bequest at the Tate Britain gallery. The evidence began to accumulate.

NE: Turner was also highly experimental when it came to pigments, all of which makes his work amenable to our techniques.

Have you been involved in analysing the work of many other painters?

NE: Yes. At the moment, for example, I’m doing a lot of consultancy work for the Russian art market. The boom in the Russian economy has brought in its wake a renewed interest from Russians in their own culture, and at the same time an increase in the number of fakes, so there is demand for this kind of analysis.

Paul, you were famously involved in an attempt to authenticate a .

PPB: Yes. on the canvas to a fingerprint on a can of paint in Pollock’s studio and to fingerprints on two authenticated Pollock canvases (see image). I found hair samples on the painting too – Pollock suffered from male pattern baldness – but they were too small for analysis. The provenance of the painting – the paper trail linking it to its maker – is unknown and it remains unsold. We are working on other possible Pollock cases where DNA is involved. I have samples of hairs from Pollock’s studio floor and I found a descendent of Pollock’s mother who agreed to donate her DNA. It matched the DNA from the hairs.

Can you ever be certain who created an artwork?

PPB: Yes, but not often. Take Picasso. He made several plaster casts of his hands, and on at least one occasion, he covered his palm with paint, pressed it inside a book cover and autographed it. In a case like that we can make a definite identification, but in most cases, the most you can say is that the print on this object matches one on that object. It is all about demonstrating connections, even if the artist may not be specifically identifiable.

Has your work ever dramatically changed the value of a painting?

NE: A good example is the that sold in 2002 for just under £50 million. It was lost for many years under another name. My scientific analysis was a key part of the documentation for sale.

PPB: We’re working on a possible Turner right now. If it’s genuine then the owner, who bought it for pounds, will be able to sell it for millions.

How has the art world, which usually relies on the intuition of art experts, responded to you?

NE: There has been resistance. Even the notion that scientific methods can be used is not universally accepted. There is a perception that art and science are in opposition, yet the latest approaches allow us to use both art history and scientific evidence to reach a conclusion. I often encounter people saying “You can’t tell anything from pigment analysis. It’s too broad. You don’t know enough about what everybody else was doing at the time.”

“There is a perception that art and science are opposed, but they should be complementary”

PPB: In the documentary ? a New York art lawyer questions the relevance of fingerprint evidence. I think that says it all. I grew up with art and I think intuition is absolutely relevant, because in the end how a painting looks is subjective. A person has to develop a language of seeing, a visual vocabulary, to articulate what he sees when he looks at art. The trouble is, even the highly visually aware can be fooled, and that’s where our techniques come in. Ideally, the two approaches are complementary.

Despite its resistance, the art world has come to rely on you, hasn’t it?

PPB: The provenance of a painting has always been important in the buying and selling of art. But faking a provenance is far easier than faking the art itself, so now, as well as the usual documentation, a buyer wants to know the results of a scientific analysis. The seller knows he’s wise to have had that analysis done. The mindset has changed over the last 20 years.

Is demand for your services growing?

PPB: Yes, especially as the world becomes embroiled in financial turmoil. As people lose faith in currency and investment schemes, they turn to blue-chip art – the secure, high-value art that you know you can buy for a million and sell for a million.

What can you do if you suspect the heirloom hanging on your wall is a lost masterpiece?

NE: The problem is getting heard. Specialists on big names like Constable or Rembrandt are being approached all the time, and sorting the good from the bad is time-consuming for them. People like us know how to present your case to the art world. We can steer your painting through the many pitfalls that exist between the wall at home and the wall in the museum.