Retro Review - 2000 - Microscopy of Stone Cylinder Seals

Retro Review - 2000 - Microscopy of Stone Cylinder Seals

Monday, March 3, 2008

Keywords: scanning electron microscopy, lithic microflaking, stone carving
Other than the obsidian tools, some of the coolest artifacts discovered at the archaeological site where I work in northeastern Syria (Tell Mozan, ancient Urkesh) are cylinder seals. The small cylinders are typically made from stone or minerals like lapis lazuli, hematite, steatite, and chalcedony -- some are even made from obsidian! The carved seals were rolled onto clay and left behind an impression of a scene. Some show battle scenes. Others show kings and queens. Athletes, hunters, and mythical figures are also depicted. You can also find replicas of racy cylinder seals for purchase online. The detail in many of these seals is really impressive, and their patterns often wrap around to form continuous scenes. The researchers in this article from 2000 used scanning electron microscopy to examine Mesopotamian cylinder seals and determine how these fine designs were carved. They concluded that the skilled craftsmen (and women?) were filed and microflaked, not cut or engraved with a wheel (somewhat like a tiny pizza cutter), as was previously thought. The experiments also suggested that, during the third millennium BCE, the seal carvers used copper tools and powdered quartz as an abrasive. Later during the next millennium, copper and/or bronze tools were instead used with emery, that is, impure corundum (aluminum oxide) usually containing iron oxide, either magnetite (Fe3O4) or hematite (Fe2O3). If you would like to see some cylinder seals and aren't heading to the Middle East anytime soon, the best collection that I have seen sits in the Metropolitan Museum of Art -- you can also view some of them on the Met's website.
Above: Mesopotamian cylinder seal carved in albite, circa 2350-2150 BCE. Credit: Metropolitan Museum of Art.
Excerpts from Science News:
Ancient Seal Technology Shows Its Age
By Jessica Gorman
Somehow, ancient Mesopotamians carved elaborate scenes on the sides of crystal cylinders just centimeters tall. They even did this in reverse, so a cylinder would imprint its owner's mark when rolled across soft clay.
Archeologists have long guessed at engravers' techniques by studying their designs. Now, researchers have used modern technologies to illuminate the ancient ones, and they've found that Mesopotamians adopted one of their most efficient engraving methods some 1,500 years later than thought. . .
Over the millennia, new technologies arose for carving harder materials. Wheel cutting, the most efficient method for cutting tough varieties of quartz, used a tiny engraving disk at the end of an axle, which the engraver powered with the sawing motion of a bow. During the past 30 years, archeologists had placed the onset of this technology in the second half of the fourth millennium B.C.
Sax and her colleagues used scanning electron microscopy to identify the signatures of microflaking, filing, drilling, and wheel cutting in moldings of engravings they made themselves. Then they made silicone molds of many of the museum's 400 quartz seals and compared the microscopic features. Their results, published in the June Antiquity, show that the engraving wheel probably didn't make its debut until the middle of the second millennium B.C.
Some features archeologists previously believed were due to wheel work were actually microflaked or filed with different tools, says Sax. . .

To read the rest of the article, visit the Science News website (subscription required):
http://www.sciencenews.org/articles/20000715/fob3.asp

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