For centuries, the ability to distinguish forged works of ancient art from the real thing was exclusively the province of scholars and connoisseurs. Through decades of study, they developed an eye for minute details of style and iconography that provided clues to a work's authenticity. Scholarship was at least partially effective in ferreting out fakes.
But not completely. Too often, the works of highly skilled forgers - artists in their own right - were successfully passed off as genuine antiquities. In many instances, scholarship alone was not sufficient to give definitive proof of a work's authenticity.
Over the past 30 years, science has revolutionized the art of authentication. Using X-rays, gamma rays, scanning electron microscopes, and other modern equipment and techniques, scientists have teamed up with art historians to erect a formidable barrier between the art forger and the art museum.
Many of the scientific techniques and art historical methods of authentication are part of an exhibition that opens this Friday at the Nelson-Atkins Museum of Art in Kansas City, Mo. Titled "Discovery and Deceit: Archaeology and the Forger's Craft," the show is the largest ever of its kind in the United States. It consists of about 40 genuine antiquities, masterpieces from the ancient civilizations of Greece, Rome, Egypt, and the Near East. These are interspersed with a roughly equal number of modern-day fakes, forgeries crafted with such expertise that they were unwittingly acquired by leading art museums and private collectors as the real thing. Also on view are a handful of genuine antiquities that have been "improved" by modern craftsmen, as well as several suspected forgeries that have recently, with the help of science, been proved authentic and resurrected from storage to display.
The show was organized by Robert Cohon, the Nelson's curator of ancient art and a professor of art history at the University of Missouri-Kansas City.
While Dr. Cohon has been fascinated with the subject of forgery since his graduate-school days, the idea for this exhibition crystallized 10 years ago. At this time, he discovered that students in his night classes on ancient Greek sculpture - working adults who often found it hard to stay awake during an evening class conducted in a room darkened for slide projection - were fascinated with forgeries.
"I showed them a slide of a sculpture and had them date it by style and iconography. I got a few halfhearted answers," he said in a recent interview. "But when I told them that the sculpture was probably not a masterpiece from 530 BC but a forgery from 1960, then I had their attention."
Studying fakes caused his students to view objects with much greater interest in the small details. Cohon decided to try a similar thing in a museum exhibition. About one-third of "Discovery and Deceit" is devoted entirely to explanations and hands-on displays of the scientific techniques that are used in authentication.
Some of the equipment is relatively simple. A magnifying glass can reveal a surprising number of clues. In the center of the room, four marble heads rest on a display table. Museumgoers can put the lens of the magnifying glass right up to the stone and see the smooth, polished surface of a forged head, as opposed to the naturally weathered surface of a genuine ancient sculpture, where the smooth surface has been worn away to reveal a crystalline structure resembling sugar.
Some techniques, like the thermoluminescence (TL) test, are not so simple. The TL test measures the light given off by baked clay, or terra cotta, when the clay is exposed to intense heat. The amount of light emitted shows when the clay was originally baked. The less light, the more recently it was baked.
"The TL test has been extremely valuable to museums," says Cohon, "because terra cotta, a common material in ancient times, is notoriously difficult to date." It is fairly easy to make a mold from a genuine terra-cotta sculpture and produce copies, and many high-quality forgeries were made in this way in the late 19th and early 20th centuries. The Nelson exhibit contains two virtually identical terra-cotta figurines side by side. Only through TL testing can one be proved to be from the 3rd century BC and the other to be a modern copy.
Also on display are numerous enlargements of X-radiographs, gamma radiographs, and images taken from scanning electron microscopes. These enlargements reveal subtle clues that can't been seen with the unaided eye. For instance, an X-ray of a supposed Sasanian dish from the 6th century AD reveals air bubbles, indicating that two metal pieces were joined together with solder, when it is known that the Sasanians fashioned their dazzlingly beautiful - and extraordinarily rare - dishes from a single piece of gilded silver.
Viewers can also look at several sculptures and a vase in ultraviolet (UV) light boxes. Certain paints, both ancient and modern, are known to fluoresce when exposed to ultraviolet light. Viewers can see an authentic Egyptian relief under natural light, then push a button and see it under UV light. The eyes of the figures in the relief glow under UV light, indicating that the piece was retouched with a paint unknown to ancient Egyptians.
In another light box, the fluorescing of the mantle of a small Greek terra-cotta figure proves that it is authentic. In the latter case, the rosy hue of the glowing paint indicates the presence of roseaster, an element used in ancient, not modern, paint.
The highlight of the science room of "Discovery and Deceit" is a case study of the head of a Roman girl, a gift to the museum in the 1970s. Cohon suspected for years that something was wrong with it. The cranium was too big for the face and, unusual in a portrait, the hair was carved in greater detail than the face. Most of all, said Cohon, "She has a Victorian nose." Gamma rays (which are like X-rays, but strong enough to penetrate stone) revealed the head to be essentially genuine, but with a great deal of later restoration.
In a series of photographic and gamma-ray images that reveal much of the additions and augmentation to the head, viewers are led step by step through the process of authentication and can see how the various clues are put together to arrive at a final conclusion. This demonstrates how art history and hard science combine to solve the mystery.
Cohon estimates that scholarship and science each contribute about 50 percent to the authentication process.
A few art historians, those from the pre-technology days, are less than thrilled with this development. They say that some of the sport has been taken away when sophisticated equipment is brought in to supplement the discerning eyes of the connoisseur. Cohon appreciates this feeling, but welcomes the addition of science to the scholars anti-forgery arsenal.
"A little bit of the glamour has been taken away," he acknowledges. "Me? I take hard science over glamour any day."
* 'Discovery and Deceit: Archaeology and the Forger's Craft' is on view at the Nelson-Atkins Museum of Art in Kansas City, Mo., from Oct. 11 through Jan. 5, 1997. It reopens at the Michael C. Carlos Museum, Emory University, Atlanta, on Feb. 8, 1997, and closes on May 18.