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Conservation Scientists Get Into The Vibe

Raman was used to identify the arsenic-based pigment on this Egyptian mask. Credit: Peter Vandenabeele

This week some 120 conservation researchers are facing the tragic hardship that comes from spending a week in Parma, Italy, where there is a conference called “Raman in art and archeology.”

This is not a conference about art made from tasty Japanese noodles. (That’s Ramen, silly!)

But if you caught the gratuitous pun in my headline, then you probably already know that Raman spectroscopy is an analytical technology that helps scientists study the vibrations and rotations that occur within molecules. Conservation scientists get giddy about Raman for a bunch or reasons, Peter Vandenabeele, an organizer of the conference, told me:

First: Raman is not picky about art. Which is to say that the technique can be used to study the chemical make-up of jewelry, oil paintings, Egyptian burial masks, glass, Mayan wall paintings… you get the picture.

Second: Portable Raman spectroscopy equipment is non-invasive, so it doesn’t hurt artwork. Scientists head to a museum, and shine low frequency laser light at a painting or sculpture which has mysterious molecular components that they want to know more about—such as a pigment that gives artwork brilliant color, or a pigment that is fading with time.

Shining the light on the artwork makes the molecules inside vibrate. As the molecules eventually relax they release photons of light that scientists can then measure. These photons are a chemical fingerprint that reveals the identity of the molecule that was vibrating. So researchers can learn about the molecular make-up of the artwork without touching it, except with some low energy laser light.

Using Raman to study pigment used in old texts. Credit: Peter Vandenabeele

Third: Raman is a non-invasive technique that can provide more information about art than other hands-off methods, such as X-ray fluorescence, where conservation scientists shoot X-rays at art and get it to fluoresce.

This X-ray fluorescence gives scientists information about the artwork’s chemical elements… such as the presence of arsenic, zinc or sulfur. This is obviously useful information, but sometimes a particular element—say arsenic—is present in a several types of different pigment molecules found on artwork. Using X-ray fluorescence you can find out that there’s an arsenic-based pigment inside, but you don’t know which one. Raman can get you the name of the pigment, such as realgar which is a pigment composed of both sulfur and arsenic and used in ancient Egypt.

Now for the downside: Although Raman isn’t picky about the types of art it can study, the technique can be a royal pain-in-the-butt to get working in the field (or museum). Vandenabeele told me that, in particular, it can be extremely time consuming to properly focus the Raman equipment so that you actually get useful data. In contrast to X-ray fluorescence, where conservation scientists just point an X-ray gun at artwork to learn about the elements inside, Raman can be much more fiddly.

I’m guessing that researchers at the conference will be sharing tricks for getting Raman operating on a potpourri of cool art and archeology objects. And I suspect they’ll be contemplating other artful mysteries, such as the genius that is tortelli d’erbetta covered in Parmigiano cheese or a perfect slice of Parma ham.

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