Rembrandt painted 700 pictures. Of these, 3,000 are still in existence.
-Wilhelm Bode (art critic, 1845-1972)
Ever been to an art museum with your class or family and seen a local artist propped up next to a masterpiece by a big name like Picasso, painting a replica that is virtually identical to the original?
Well if any artist can paint something so similar to a masterpiece, how does the museum in fact know that the one hanging on the wall is actually the original and not a fake?
It’s the role of a museum curator or art appraiser to determine if a painting is real or fake. Like a detective, they look for clues, mostly in the painting itself. Familiarity with what and how the artist paint is important, but the modern art detective has access to scientific instruments and techniques which can give a lot of other useful information.
For example, if the chemicals that make up the paints, inks, varnish and other parts of the painting are discovered, they can be compared to what paints the artist probably used.
Knowing how many layers of paint make up a painting can also help determine the condition of a painting such as whether it’s been repaired, restored, or painted over. All of this information is important to tell if a work of art is indeed authentic!
The trick is to collect these clues without destroying too much (or any) of the painting. One of the best ways to do this is with an electron microscope.
An electron microscope is a very powerful type of microscope that bounces electrons or X-rays off a small sample (in this case, taken from a painting). The sample can be as small as a piece removed with just the tip of a needle!
So how does the microscope get information we can't see? As you know, we are able to see a painting by visible light that bounces of the painting's surface. X-rays, however, vibrate much faster than visible light even though they are part of the same electro-magnetic spectrum.
So X-rays would show different things than visible light, if only we could seen them. With a short enough wavelength, x-rays can even penetrate past the upper layers of the painting to reveal what's underneath.
Since different chemicals have different crystal structure or makeup, they absorb or reflect rays differently. The X-rays that bounce back are recorded by detectors built into the electron microscope which can then be read by the art investigator. It is this information that give additional clues as to the chemical makeup of the painting.
Did You Know?
The general term for the detection of the “spectrum” of visible and invisible radiation as a means to study objects is called “spectrometry”. Spectrometry instruments use visible or invisible rays (including x-rays, ultraviolet and infrared rays). Luckily for curators, some of these types of equipment are portable so they can be moved around to different museums. Some can even operate directly on the painting so a sample doesn't have to be taken from the art piece. This equipment might go by different names depending on exactly what it does, for example, an “X-ray spectrometer”…
This technology has been put to use all over the art world. For example, the Canadian Conservation Institute used X-rays to measure the diffraction (bending) pattern of chemicals in a picture said to be painted by the famous painter Van Gogh. What they found was a form of titanium oxide in the paint which was unavailable during the artists' lifetime, indicating that painting was not a Van Gogh
A more famous case is the “Vinland map” - a map that detailed the paths of early Viking explorations, said to be copied in the 15th century. In this case, infrared light was used which detected the presence of an ink made from carbon. This finding helped lead the scientists to conclude that the map was a fake and was actually made after 1923!
With advanced equipment and methods, we still need trained and intelligent people to interpret the evidence and decide what it all means. Even today, for example, a few people will use other evidence to argue the Vinland map is in fact genuine.
Canadian Conservation Institute
The Vinaland map
Analysis of Pigmentary Materials on the Vinland Map and Tartar Relation by Raman Microprobe Spectroscopy Katherine L. Brown and Robin J. H. Clark Anal. Chem.; 2002; 74(15) pp 3658 – 3661
Polarized Light Microscopy in Conservation: A Personal Perspective, by Walter C. McCrone, Journal of the American Institute for Conservation 1994 33(2) pp 101-114.
Analysis of Pigments and Inks on Oil Paintings Using Total Reflection X-Ray Fluorescence Spectrometry by R. Klockenkamper, A. von Bohlen and L. Moens, X-Ray Spectrom 2000; 29, pp 119-129
Dr. Ed Brown is a professor of Computer Science at Memorial University of Newfoundland and a technology lawyer. He spends his time thinking about why people like or don't like to use computers. You can find him at email@example.com.