Color Detective

When a new pigment like YInMn is made (see the article New Blue in the 11/21/16 issue of Science World), conservation scientist Narayan Khandekar snaps up a sample. He adds it to the pigment collection he oversees at the Harvard Art Museums in Cambridge, Massachusetts.

Pigments are substances that absorb and reflect different wavelengths, or colors, of light. They can occur naturally in minerals or plants, or they can be created in a lab—as YInMn was. Throughout history, people have chosen pigments for their bright or unique colors. The pigment collection at the Harvard Art Museums, which was started in the 1900s, now holds about 2,500 samples from around the world.

Art experts use the pigments in the collection as standards, or established norms, with which other pigments can be compared. Having a vast reference library of pigments helps conservators restore and preserve aging or damaged artworks. By studying pigments’ chemical compositions, they can better understand why paint on artworks has changed over time. Khandekar spoke with Science World about the pigment collection and how he has used it to determine whether works attributed to famous artists are authentic or forgeries. 

In the Middle Ages, a period that lasted from the 5th to the 15th century, the deep-blue pigment ultramarine used to be more valuable than gold. That’s because it came from crushing up a gem called lapis lazuli. 

Another one, mummy brown, comes from the weirdest source. It was used in the 1800s and collected by scraping substances off the bandages used to wrap ancient Egyptian mummies. Dragon’s blood has the strangest name. It’s a bright-red resin. The sticky substance comes from the leaves of a rattan palm. It got its name from a myth that the pigment could be collected only from blood spilled on the ground when dragons and elephants fought one another.

I recently worked on a series of panels by the 20th-century American artist Mark Rothko. Some of the panels had faded. My team took a sample from each painting to determine the pigments they contained and learn how and why their colors had deteriorated.

Another time, we were asked to confirm whether a newly discovered painting attributed to the American painter Jackson Pollock was authentic. We tested a sample from the painting and determined that it contained a pigment called PR254, which was used to give Ferrari sports cars their characteristic red color. This pigment wasn’t discovered until after Pollock’s death in 1956, which means he couldn’t have painted the piece.