Daguerreotypes, the earliest photographs ever taken, are fading under the concerned eyes of museum curators. To preserve these historic snapshots, scientists are probing their elemental makeup. The universal chemistry of corrosion they’ve identified could help save the pictures—and safeguard electronics of the future.
Volker Rose, a physicist at Argonne National Laboratory in Illinois, uses powerful X-rays to observe chemical changes in historic artwork. He began with Picasso. Teaming up with historians from the Art Institute of Chicago, Rose analyzed zinc oxide in Picasso’s works. He found that the artist had used common house paint, not traditional oil paints, to create shiny smooth whites in famous pieces like The Red Armchair (below). The aging pigments foretell the fates of modern nanomaterials in cellphones and solar panels, which also rely on zinc oxide. Studying how the paint weathered, says Rose, can tell us how newer technology will stand the test of time.
Rose then collaborated with the Smithsonian Institution to analyze corrosion on 150-year-old daguerreotypes. Rose and his colleagues published a paper last year on the composition of zinc white in Cubist paintings. He presented his work on the chemistry of these iconic paints and daguerreotypes at the February 2014 meeting of the American Association for the Advancement of Science in Chicago. After the symposium, he joined SciCom’s Jyoti Madhusoodanan for a penetrating discussion.
What can you see with these high-power X-rays that you can’t with other technologies?
X-rays can have different energies, from very low to very high. There is a threshold around 3,000 keV [kiloelectron volts]—everything that’s higher is called a hard X-ray. The higher the energy, the deeper you can shoot into a sample and extract information. The material reacts by sending out fingerprints of secondary radiation that we pick up. A fingerprint is unique to each element. For instance, the radiation from a cobalt cluster is different from the one from an iron cluster.
The other advantage, specific to the hard X-ray nanoprobe, is that we can focus the X-rays on a pixel. In principle, we can distinguish between different oxidation states of iron, zinc, copper and so on. Synchrotron technology [using intense X-rays spit out by powerful, circular particle accelerators] opens up a totally new avenue for studying these materials.
It’s like a new way of looking at the same painting again.
Yes. It’s actually looking deeper, picking up information that was not accessible before. The technology used until now didn’t have the ability to study at this small scale.
What was it like to work with these paintings?
We didn’t study the whole painting. The Art Institute took the samples. We were interested in looking into one single pigment, so we didn’t need the whole painting—just a tiny sample, like the head of a pin. The pieces are almost like dust.
For a lot of our research, we make our own samples, hundreds or thousands if needed. So if something happens to them, it’s no big deal. For the Picasso sample (bright white pigments, left), the number was drastically reduced. We are also studying extremely precious samples in other areas. I had one researcher come to me to study one particle of stardust, 10 microns [0.01 millimeters] large.
But from a chemical perspective, we were just studying zinc white here, a piece of paint. Zinc oxide is something we study all the time for its potential as a display material in solar cells, or as a potential replacement for all the silicon electronics we currently use.
Is there something you can extrapolate from the painting to modern technology?
Yes, that’s an important point. People like you, people who pay taxes, might ask why a Department of Energy laboratory is studying Picasso's paint.
We learn something about zinc oxide that has applications in areas that are not cultural heritage at all. For example, the impurities in zinc oxide in this sample tell us how these might behave in advanced electronics.
A lot of physicists study zinc oxide as a so-called dilute se