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explainer: Answers to your questions about the news.

Fake Out!How forgers made grime seem ancient.

By Brendan I. Koerner
Posted Thursday, Dec. 30, 2004, at 6:45 PM ET

The Israel Antiquities Authority has advised museums worldwide that their Bible-era relics may be fakes produced by a team of forgers now under indictment. These forgers are charged with concocting the so-called James ossuary, which purportedly held the bones of Jesus' brother. According to the AP's account, they were skilled at creating "ancient grime" that fooled many scientists into authenticating their wares. How might a forger go about making grime that seems ancient?

For starters, with a bit of chalk and water. The forgers' key to tricking the archaeologists was crafting an authentic-looking patina. Like copper or bronze statues, which develop a green sheen after years of oxidization, stone slowly builds up a layer of geological soot as the centuries reel by. This is caused by the chemical reaction of elements like air or water with the minute traces of metals and other elements within the rock. To the naked eye, a thick patina is an immediate sign that an artifact is aged.

Yet a skilled forger can fake a stone patina, at least convincing enough to fool all but the most advanced analysis. In the case of the James ossuary, for example, it's alleged that the forgers took an authentically old box that was inscribed simply "James, son of Joseph." According to Avner Ayalon of the Geological Survey of Israel, who studied the ossuary, the forgers may have then added the inscription "brother of Jesus" to the end of the sentence and used a solution of chalk and hot water to create a coating of calcium carbonate—a substance frequently found in stone artifacts excavated in and around Jerusalem. On cursory inspection, the patina appeared to be legitimate. Conventional verification means like ultraviolet light or simple chemical analysis could not differentiate the patina covering the first half of the inscription.

Ayalon became suspicious, though, when he tested the patina's isotopic ratios—that is, the number of oxygen atoms containing 16 protons plus neutrons versus the number of oxygen atoms containing 17 or 18 protons plus neutrons.* These ratios are affected over time by an object's environmental conditions. Ayalon discovered that the portion of the patina covering the first part of the inscription was marked by an isotopic ratio consistent with Jerusalem's groundwater. The section covering the latter half, by contrast, betrayed evidence of having been created at high temperatures, probably well in excess of 120 degrees Fahrenheit—far above the temperature of ground water in caves, where ossuaries were stored.

Strategies for crafting a convincing artificial patina can, of course, vary. Another alleged work of the indicted men was the so-called Jehoash (or Yoash) tablet, inscribed with what appeared to be proof that it had come from the 3,000-year-old Temple of Solomon. The tablet initially passed muster when chemical analysis revealed that trace amounts of carbon within the rock were, indeed, several millennia old. Furthermore, the patina featured traces of gold, and the temple was renowned in the Bible for its overlay of high-quality gold.

But questions arose when further analysis was undertaken and it was discovered that the patina was imbued with microscopic marine fossils—quite odd, considering the temple was nowhere near the sea. Then one of Israel's top archaeologists, Yuval Goren of Tel Aviv University, found that the patina on the tablet's back was made of silica rather than calcite, which would have been consistent with Jerusalem's geology. (There were also several linguistic cues that tipped off researchers, particularly anachronisms.)

Professor Goren proposed that the inscription had been chiseled onto a slab from a Medieval castle built by crusaders. A fake patina may then have been created by crushing up bits of identical stone, mixing the powder with water, and baking the whole concoction. Charcoal bits stolen from Jerusalem archaeological digs or university museums could have been added during the process, as could have specks of gold. It may have been more elegant than adding silver black to jewelry, a common trick used by charlatans to make new pieces look old. But it wasn't quite perfect.

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Correction, Dec. 31, 2004: An earlier version of the story incorrectly described oxygen atoms as containing between 16 and 18 protons. All oxygen atoms contain eight protons; those numbers reflect the atoms' combined total of protons and neutrons. Return to the corrected sentence.