Is the work of art genuine? The answer is no longer determined by art historians and connoisseurs, but by spectroscopes. On the arms race of forgers and collectors.
In 1930 the physicist C V Raman won India's first Nobel Prize for his work on the scattering of light. How surprised he would be to find that in the 21st century the spectroscope that bears his name is routinely used to help identify forgeries or misattributions in the work of great artists from Leonardo to Jackson Pollock.
The Raman spectroscope's special power is that it can analyse minute quantities of solid or amorphous substances - the minerals in pigments, for example - without damaging the object, and can be used in relatively normal atmospheric conditions.
It really came into its own when used with the intense beam of the laser, which became commercially available from the 1960s. Along with technology such as X-ray fluorescence (XRF) spectrometers, multi-spectral imaging cameras, radiocarbon and isotope dating and dendrochronology, it is part of an arsenal of scientific tools used as much in criminal forensics as in the rarefied world of fine art investigation.
Philip Mould, who with his wife Catherine runs a gallery on London's exclusive Pall Mall and has been selling British art and Old Masters for the past 30 years, saw the allure of this little-known aspect of the art world. In 2011 he pitched an idea that became Fake or Fortune, one of the most successful arts programmes in the history of the BBC, examining the provenance of artwork claiming, or hoping, to be original.
He observes that with highly detailed imagery and information widely available online 'it's a marvellous period of development for the art world, for understanding the trials and tribulations the artist has gone through over the centuries'. But these resources are equally available to forgers, who up their game accordingly. 'Fakery is an arms race,' he says simply, 'And it's getting more and more sophisticated.'
This is where science comes in: as one Californian art dealer writes: 'A good forger attempts to deceive the naked human eye. It's part of the challenge of the game he plays. Deceiving science in expert hands is, however, practically impossible.'
Tech can identify pigments, for example, which existed in specific eras: lead white was used for centuries, until it was found to be poisonous in the late nineteenth century and by the 1920s artists were using titanium white. Naples yellow was used in the 1500s, but cadmium yellow only after 1817. Acrylics appeared from the 1960s.
Dr Johann Kräftner, director of the Liechtenstein Princely Collections since 2001, has recent experience in the subject of science in art. In 2016, as widely reported in the art press, an exquisite nude of Venus, attributed to the sixteenth-century painter Lucas Cranach the Elder and bought for the Collections not long before, was one of several artworks caught up in what became known as the 'Old Masters' Scandal'.
The confiscated work has been returned and may not be discussed while the court case continues, but Dr Kräftner is convinced of the value of technology in assessing provenance, the definitive history that links a work to an artist and confirms it as original. 'We always try to fix on the scientific, rather than stylistic, research,' he says, 'Science is the only thing that can really prove if it's from the period or not.'
In an ideal world, every artwork would possess a clear pedigree and biography: the artist's signature or paperwork, bills of sale from respected galleries, mentions in wills or letters, a photograph of the artist at work, creating a chain of transactions stretching from its creation to its present owner, as incontrovertible as a genome.
Fat chance. Proving provenance is surprisingly difficult: long-dead artists can't confirm they created a work, very early works were rarely signed anyway, and even once they were a successful artist might not sign his or her work or might, like Lucas Cranach, use a stamp, several versions of which might be used by a large workshop. Struggling artists re-used canvases. Restoration work added anachronistic materials.
Add to this the fact that there is a thriving market in antique materials - coins from shipwrecks, unused sketchbook pages, old wood panels, old bronzes - and the fact that serious forgers might well have a scientist on their side, and it's not easy.
Even documentation is tricky. Before science got involved, the most reliable source of information was an artist's catalogue raisonné, the definitive record of all known works created by an artist, each of which is allocated an identification number. The earliest example is probably A Catalogue and Description of the Etchings of Rembrandt Van-Rhyn, published in Paris in 1751, and that was 80 years after the artist's death.
While appearance in a catalogue raisonné can spectacularly transform the value of a work, they are not necessarily 100% reliable. Even if an artist is alive, they may not remember accurately - or honestly. If the catalogue is compiled by interested and knowledgeable parties, from family members to independent scholars, who does the peer reviewing? And do the compilers take responsibility for any misattributions?
No wonder the auction house Sotheby's bought the scientific research company Orion Analytical in 2016 and most public galleries have their own research teams.
There is another issue for the smaller potential buyer checking provenance. 'It's expensive,' says Philip Mould, 'And there's far more tech around than there was in the past. We used to take things to the Accident and Emergency Department of the local hospital to use the X-ray machine. Nowadays we do a lot with the Courtauld Institute and their Department of Conservation. They have really got going on this.'
The Princely Collections use a small network of experts, from a semi-retired dendrochronologist who can check a wood panel against his database and say where the tree was from and when it grew, to the Hamilton Kerr Institute in Cambridge for craquelure - the network of hairline cracks on the surface of a painting - or the Curt-Engelhorn-Zentrum for Archeometry in Mannheim, for which there is a long wait.
'You need huge resources,' says Dr Kräftner, 'This work is complicated and time consuming and we are a small team. You also need time - and the private market is really fast. By the time you've done the research, the painting has gone.'
In the end, the old maxim holds true: caveat emptor (buyer beware!). In the words of one experienced dealer: if the deal is too good, there's probably something wrong.'