MICHELE NORRIS, host:
From NPR News, this is ALL THINGS CONSIDERED. I'm Michele Norris.
Haven't thought much about crystal skulls recently? Well, they're going hard to avoid once the new Indiana Jones movie opens this week. It's called "Indiana Jones and the Kingdom of the Crystal Skull." That skull is the latest artifact the tough guy archeologist is seeking and it just so happens there actually are crystal skulls - some in museums, some held by private collectors.
As NPR's Christopher Joyce reports, they are mysterious, but not in the way Hollywood makes them out to be.
CHRISTOPHER JOYCE: Way back in the inner recesses of the Smithsonian's Museum of Natural History in Washington, D.C. - down a hallway lined with ceiling-high cabinets filled with human bones - there's a large office. And in one corner there's an old metal filing cabinet.
(Soundbite of cabinet drawer)
JOYCE: And inside that cabinet is a crystal skull.
Ms. JANE WALSH (Smithsonian Anthropologist): This is actually called milky quartz.
JOYCE: Using both hands, anthropologist Jane Walsh gingerly lifts a carved skull the size of a bowling ball.
Ms. WALSH: It weighs 31 pounds. I know because I carried it to London.
JOYCE: The skull came to the Smithsonian Institution in a mail in 1992. The anonymous donor said it was a genuine artifact of the Aztec Empire, which collapsed in the 1500s. Now, the crystal skull in the new Indiana Jones is also supposed to be ancient and of great value.
Walsh wondered if her skull was the Real McCoy. She did some reading and discovered that there are dozens of crystal skulls around the world; most are quite small, the size of golf balls. They started in the antiquities trade in 1860s. Several were sold from Mexico by a French collector named Eugene Boban.
Could the Aztecs have carved them? Walsh studied the kinds of tools the Aztecs used to carve stone. She's got one in her office.
(Soundbite of pump drill)
Ms. WALSH: This mechanism, this pump drill is basically for drilling the holes.
JOYCE: It's a wood-and-rope contraction that spins a wooden rod with a stone tip. Such tools left distinctive marks, different from the marks left by modern tools like a fast-spinning rotary wheel. Now Walsh needed someone who could help her analyze the skull, an expert in London.
Ms. WALSH: Margaret Sax of the British Museum is the one who has done the technical analysis of the carving and the polishing.
JOYCE: Walsh took her 31-pound skull to Margaret Sax. Sax examined the tool marks under a powerful microscope. She had done the same with another big crystal skull the British Museum had owned for over a century. It too was supposed to be ancient Mexican. And what Sax found was...
Ms. MARGARET SAX (British Museum): The tool marks on both the Smithsonian skull and the British Museum skull were clearly produced by wheel cutting. And so we're able to say they are of post-Columbian date.
JOYCE: Meaning the tools were modern. The shape and depth and surface texture of the marks they left were characteristic of rotary cutting tools, and the Aztecs didn't have those. Now Walsh and Sax are looking at the type of quartz the skulls are made of. Small imperfections can identify where they came from. They say neither of the two skulls is likely form Mexico, home of the Aztecs.
One thing the scientists have figured out is that the British Museum skull came from Eugene Boban, that mysterious French collector. In the late 1800s, he first described it as a piece of artwork, then as an Aztec artifact.
Ms. SAX: You must bear in mind that he couldn't sell it. So he did need to make it more appealing in order to sell it.
JOYCE: So what are these things? Walsh says they're not exactly fakes because they aren't copies of anything.
Ms. WALSH: I don't think there are any real ones. They're really a kind of invented artifact, some person or some workshop was cranking them out and selling them to a European or North American audience, which is where they all wind up.
JOYCE: Eventually to be locked up way back in the bowels of a museum.
Ms. WALSH: We should have him face out. People keep telling me not to look it in the eye.
Christopher Joyce, NPR News.