Art as a chemistry project

Scientists who toil in the field of art conservation are detectives at heart. The “criminals” they chase in most cases are simply age and negligence.

Their work is crucial, because before their peers — the conservators — attempt to restore or preserve an item, scientists often are called upon to analyze its contents. In addition to helping conservators decide how best to treat and protect a work, their findings can become the springboard for fresh investigations.

Over and above conservators’ hands-on skills, scientists need to know the standard form of materials under study and be able to recognize what is novel or unusual about the composition of an object, whether sculpture, watercolor, painting or any combination of these. In this way, they can go where no one has gone before, doing pure research. On good days, they discover new facets about an artist and his technique.

Because they often grapple with estimating an artist’s intentions, even one who lived hundreds of years ago, their job seldom is dull.

Advances in technology have eased the task in many ways, but research scientists employed by the Conservation Department at the National Gallery of Art insist it would be wrong simply to credit progress in their field to the ingenuity of engineers.

“Application is the secret rather than the machine,” says Barbara Berrie, senior conservation scientist in the Scientific Research Department, who holds a doctorate in inorganic chemistry. “It’s knowing what you are looking for and asking the right questions.”

“It is terribly exciting. You go to a museum and see this wonderful illusional image on the wall, and what we get to do is study what it is composed of — without taking away the mystery,” says Ross Merrill, whose title is chief of conservation.

“Someone once asked how long it took to analyze a painting, and the answer was about three times as long as it took the artist to do it. Often you can look and see whether the work was quickly executed or not.”

He praises rapid developments in imaging and other marvels of the digital age but doesn’t rush to introduce new techniques “until they have proven their worth and value” — at least where the painting lab is concerned. “When we are getting a painting ready to do conservation, we do a technical study that often raises more questions than answers,” he says.

Conservation activities and scientific treatment at the gallery come under one administrative structure, to include eight or more full-time scientists and 30 conservators. Scientists such as Ms. Berrie have specialties, mostly having to do with organic or physical chemistry. This allows for “different approaches to the same problem on the same issue,” in Mr. Merrill’s words.

“You have to know a lot about instrumental analysis and a lot about the history of artist materials,” says Ms. Berrie, who compares the nature of her job to that of being a member of an orchestra. “We all play our instruments, but they come together. We have to put everything together. That sounds a bit coy, but it is like that.”

One of these “instruments” is called simply the HPLC, short for the high performance liquid chromatography process first developed in the medical world. Conservation scientists use it to help identify the kinds of dyes found in various paints. Because it requires taking a sample of paint and dissolving it in a solvent, the method is regarded as an “invasive” or “destructive” technique and is not ideal for obvious reasons.

“Except,” as Ms. Berrie points out, “the work [likely a painting, drawing or watercolor] usually is not in great shape to begin with, having lots of cracks. So when we take a sample, we work with the old damage.”

Paintings under study first are examined using an XRS — an X-ray fluorescent spectrometer — for an elemental analysis of color. The measurement of characteristic X-rays tells which chemical elements, such as lead, mercury, chromium or tin, are present in the pigments. (Dyes and pigments both impart color, but a dye usually is liquid, while basic pigments are dry.)

A tiny sample from the work is needed when using a high-resolution scanning electron microscope, known as the SEM, that can photograph in detail the physical structure of a pigment particle — within limits. It has been used for 12 years in the gallery’s lab and applied in the conservation field for about 20 years, Ms. Berrie says.

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