A Case of Art Fraud Unmasked

Skip Palenik ¹

An interesting application of analytical microscopy is the detection of art and archaeology hoaxes. The benefits of a microscopical approach to these problems arise not only from the capacity to deal with microscopic samples but also the "resolving" ability of the microscope to distinguish a small inhomogeneity and exploit it. Such was the case in a recent problem submitted by a long time client of ours who is a dealer in prehistoric art with galleries in New York city. He explained that while on a buying trip in Switzerland, he had the opportunity to examine an extraordinary early Greek bronze statue which was being offered for sale at a reasonable price. The item, if authentic, would be the world's best example of this particular subject, exceeding that of the best example known at the time, which was displayed in a museum in Turkey. The price, however, was reasonable which made him cautious.

The studio which offered the item for sale permitted him time to examine it and to take small samples to help in his purchase decision. Our dealer originally trained as a metallurgist and conservator and was used to taking small samples. During his inspection of the entire object with a low magnification stereomicroscope, he noticed what appeared to be an encrusted fiber sticking out of the patina which covered the surface of the statuette. Using a pair of forceps, he broke off a small piece of the corrosion which contained the encrusted fiber. He sent the specimen to us on his return to New York.

The sample which we received consisted of a small quantity of particles of a blue copper corrosion product. One of these had an apparent fiber sticking out of it (Figure 1). Previous experience with ancient fibers trapped in corrosion products on coins and other archaeological specimens taught us that there may or may not have been a fiber inside. In previous cases these have ranged all the way from intact fibers (usually wool or cotton) to pseudomorphs where replacement by the corrosion minerals is complete. Most archaeological fibers fall somewhere in between, but in almost every case where there is still something remaining, it can at least be identified as a cellulosic (cotton or linen) or protein (wool) fiber.

One thing archaeological fibers all have in common is their brittleness. We, therefore, took great care to attempt to remove the fiber intact. We first isolated the particle containing the apparent fiber (Figure 2). Next we chipped away as much of the corrosion product as possible using tungsten needles while observing through a stereomicroscope (Figure 3). Finally, we used dilute acid to gently dissolve the remaining corrosion compounds, a technique which had worked well in the past on coins from ancient Carthage. The remaining fiber was washed in successive droplets of distilled water. A segment of the fiber was cut from the whole length, mounted in a drop of water, and examined with the polarizing microscope (Figures 4 and 5). The fiber was easily identified as cellulose on the basis of its morphological features and behavior between crossed polars. It was remarkable, however, because of its freshness. There ?ppeared to be little or no physical attrition to the fiber. The gradual loss of morphology is one of the most obvious characteristics of fibers recovered from corrosion crusts. This fiber looked as fresh as if it had originated from a dustball in the corner of a bedroom. Since there is nothing odd about a cotton fiber being found in an ancient corrosion product, we decided to proceed a step further. The piece of the fiber which had been cut off for the morphological examination described above was now examined with the fluorescence microscope using ultraviolet excitation. The colorless fiber exhibits the strong blue-white fluorescence characteristic of an optical brightener. Optical brighteners are fluorescent compounds (usually derivatives of stilbene) which are added to textiles to make them "whiter than white."

Their brightness is based on their fluorescence when illuminated with ultraviolet light from fluorescent lamps or sunlight. Since they fluoresce in the blue region of the visible spectrum, they appear whiter (i.e., bluer) to our eyes which regard the yellow end of the spectrum as duller or dirtier. Optical brighteners are either added directly to synthetic fibers (e.g., polyester for cotton/ polyester shirts and blouses' during manufacturing or in laundry detergents which is the way most cotton fibers pick them up. They are also added to writing and copy papers. These compounds were invented in the 1940's in Germany, but were not used commercially in laundry detergents or paper until the early 1950's.

This final observation put the matter to rest. The fiber is a modern cellulose fiber, most likely a paper fiber, which was trapped in the corrosion product as it was being formed. Thus, in this case, the corrosion product must have been formed since 1950. As it was being formed, a single paper fiber either settled out of the dust in the air or became in some other way attached to the copper salt as it was being grown on the object. Confronted with this information, the seller withdrew the item from sale. Our client was happy to have his doubts confirmed since he would have hated to miss out on such a great purchase opportunity had it been authentic.

A color photocopy of the fiber showing its blue fluorescence is available from the author. To obtain Figure 6 simply send a self-addressed envelope to Skip Palenik at Microtrace.

FOOTNOTES
¹ Microtrace, 1750 Grandstand Place, Elgin, IL 60123