Can Raman microscopy reveal art forgeries?

Chinese national Pei-Shen Qian lived in a modest house in Queens, New York. He made a meager living as an artist in the early 2010s.

Neighbors noticed his windows were always covered. And they wondered why expensive cars brought paintings to the home, instead of from it.

Qian was apparently frustrated with his failure to make his mark in New York City, the center of the art world.

Behind those window coverings, Qian allegedly created dozens of works in the style of America’s Modernistic masters, including Jackson Pollock, Barnett Newman, Robert Motherwell and Richard Diebenkorn.

A conspiring art dealer brought authentic works for Qian to study, and paid him a few thousand dollars for each of his forgeries. Those fakes eventually garnered more than $80 million in the open market.

The scheme began to unravel when a gallery questioned the authenticity of a purported Jackson Pollock painting.  Pollock was an American abstract expressionist in the mid-20^th century, known for pouring or splashing household paint onto horizontal surfaces to create his art.

Investigators used a Raman confocal microscope, which can profile tiny samples of paint. It revealed the presence of Red 170 pigment in the painting. Unfortunately for Qian and his co-conspirators, the pigment wasn’t widely available until decades after Pollock’s death in 1956. Science revealed a fraud.

The discovery uncovered a ring that included the art dealer, her family, and the owner of one of the longest running and most famous art galleries in the U.S., the Knoedler gallery. The scandal exposed other forgeries, and resulted in the Knoedler gallery’s closing. Qian fled the country and never faced charges.

Raman spectroscopy is a non-destructive chemical analysis technique that uses inelastic light scattering to identify a molecule’s unique fingerprint. It provides detailed information about chemical structure, phase and polymorphy (form and crystal structure), crystallinity, and molecular interactions.

Raman spectra are comprised of a number of peaks with differing intensity and energy that correspond to different vibrational modes within the molecule.  These vibrational modes provide information on the atoms and bonding within the material under study.

Enter Jennifer Mass and Scientific Analysis of Fine Art, LLC. She is one of just approximately 150 chemists and materials engineers working art investigators in the United States, scientists that establish the authenticity of works of art.

Mass, who has a Ph.D. in inorganic chemistry, is a cultural heritage scientist. Their jobs are to conduct scientific research into the authenticity and state of preservation of a range of artifacts, including sculptures, archeological artifacts, buildings, books and paintings. It’s an interdisciplinary field that includes chemists, physicists, biologists, geologists and materials engineers.

Mass’s company gets about four purported Jackson Pollocks a month to evaluate.

“Many artists that were working in the 40s, 50s and 60s were using a specific type of titanium white paint that was co-precipitated with gypsum, a calcium sulfate compound,” Mass said. “It was made to be a commercial paint, like a house paint, but it had this gloss that they really liked.”

Several celebrated artists used the paint in their works. That particular type of titanium white has a specific Raman signature that's different from the other titanium white pigments.

“Finding that paint or its absence can be very helpful in terms of whether or not it makes sense for a work that might or might not have been made by Jackson Pollock,” she said.

Artists make paints with a variety of ingredients, including pigment and dyes, binding media, fillers, and driers. Over time, these ingredients interact and change one another.

Each chemical has its own Raman and infrared signature, and Mass maintains a library of spectral signatures relevant to the materials, artists and periods she studies.

That includes the attribution and preservation of old 17^th century masters paintings, 19th century paintings, the early Modernists through the Expressionists, and contemporary painting.  Mass also teaches the history and identification of artists’ materials.

Verifying works of art include several subspecialties:

1. Authentication: The authenticity depends in part on the materials and techniques of the work being appropriate for the alleged age of the piece.  
2. Provenance: A lineage of ownership and chain of possession of the work of art.
3. Attribution: An assessment of who was responsible for creating a particular work.
4. State of preservation: The changes that have occurred to a work of art over time, and previous campaigns of restoration and conservation of a work of art.
5. Mechanisms of degradation: The processes of chemical interactions with the environment and molecules in the medium.

Each area contributes to the verification or disqualification of a piece of art as genuine. Scientists in her group specialize in each of these subspecialties.

Attribution or authenticity of a work of art depends in part on the materials and techniques of the work being appropriate for the purported age of the piece, according to Mass.

She extracts a minute sample of the paint - smaller than the period at the end of this sentence - from the tacking margin of the canvas. It’s the area that’s wrapped around the stretcher bar and hidden by the frame. She samples from the tacking margin so that the microsampling site is hidden from view.

“Anytime you take a sample from an object of art, you want it to be as small as possible,” she said.

The advantage of Raman spectroscopy is that she can use minuscule samples to collect molecular fingerprinting data under a microscope.

“It's such a sensitive technique, it makes it ideal for this type of research.”

Sometimes the palettes of specific artists are not available. Yet Mass will know what materials would have been available to the artists at the time when and the location where they were working.

There are also degradation mechanisms at play. The binders in the paint of a piece of art that is hundreds of years old will chemically interact with each other and with the work’s pigments and fillers. That produces more clues to the art’s age and composition.

About 70 percent of Mass’s work is dedicated to examining paintings. She spends the balance of her time on sculptures, where Raman also plays a role.

“We’re trying to understand mechanisms of degradation,” she said. “So we look at metal corrosion for example, and a range of degradation mechanisms on outdoor sculptures. We're doing a lot of pigment analysis, mineralogical analysis, and corrosion analysis.”

Mass frequently uses a HORIBA XploRA™ Plus Confocal Raman spectrometer (microscope) to analyze art.

The XploRA PLUS is fully confocal, and doesn’t compromise image quality, spatial, or depth resolution. The ultra-fast Raman imaging allows the acquisition of detailed Raman maps on second/minute timescales, with integration times down to 1ms and below.

Mass’s company analyzes and evaluates art for clients that include U.S. and European museums, galleries, collectors, international art law firms, auction houses, insurance firms, and conservation firms.

Her team of scientists provide due diligence, attribution, provenance, state of preservation and authentication data to help resolve insurance, tax, and title disputes.

Art lawyers and insurance companies might call Mass to assess a damaged painting to determine if the damage was intentional for insurance purposes, or if the painting was altered in any way to disguise its origins in the case of repatriation disputes. More typically, Scientific Analysis of Fine Art focuses on whether the art is truly what it’s represented to be.

Scientific Analysis of Fine Art recently opened a new lab in a Harlem building in Manhattan. The facility, called Arcis, is a high-tech, fortified structure that houses millions of dollars of art for inspection and storage.

In fact, the word Arcis is Latin for fortress.

The pristine, modernistic 110,000 square-foot facility sits amid residential apartment buildings on a side street of the uptown neighborhood. Its four levels contain dozens of compartments protected by retracting steel doors. Builders heavily safeguarded the facility with advanced security systems and electronic card readers at every interior door and elevator.

Engineers built sophisticated climate control systems to protect the artwork from environmental contaminants. The systems regulate temperature, humidity, light and airborne particles, all of which could damage the inventory. It creates a constant background hum in the building’s sparse open spaces.

Privacy is a critical part of the operation. In fact, administrators put the building on lock-down during the interview with Mass while another client brought in some works of art they wanted kept private.

The government classifies Arcis as a Foreign-Trade Zone, a secure area under U.S. Customs and Border Protection. Commercial merchandise, both domestic and foreign, receives the same treatment by U.S. Customs as if it were outside the commerce of the United States. It’s free of customs duties and most local and state taxes while it is housed there.

Mass said when she uncovers a copy of an artist’s work (either a forgery or a work that has had its origins lost over time), nine out of 10 times the client accepts the conclusion. Yet, 10 percent of the time, the owner or prospective buyer refuses to accept the assessment. It’s a human trait.

There will probably always be art forgers, since the potential rewards are high. But with diligence, the proper instruments, and trained scientists, the days of forgeries may be waning.

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