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The Philadelphia Inquirer
(MCT)
PHILADELPHIA - Julia Lawson's gloved hand moves with short, precise strokes, each pass of her scalpel kicking up a small cloud of ancient dust and rock particles.
Little by little, she reveals a piece of history underneath the rocky crust: a 4,500-year-old bronze knife blade from the cradle of civilization.
Spread on a table before her, in a lab at the University of Pennsylvania Museum of Archaeology and Anthropology, are dozens of similar items - fragile bowls, arrowheads and tools from the Mesopotamian city of Ur.
Most are free of hardened soil deposits and will not need the scalpel treatment, but all share the greenish corrosion common to ancient bronze.
"The more vivid the green, the more worried we get," says senior conservator Virginia Greene, standing nearby as Lawson scrutinizes her efforts through a microscope.
The Philadelphia museum is in the midst of a two-year quest to slow the effects of time, stabilizing 807 bronze and iron artifacts its archaeologists excavated in the 1920s and 1930s.
The work is seen as especially important because the items are from what is now southern Iraq, where looting of similar historic treasures is a continuing concern for archaeologists.
At least 10,000 artifacts are thought to have been spirited out of Iraq's national museum during the early part of the war.
That is far fewer than initially feared, said Richard Zettler, associate curator of the museum's Near East section. But elsewhere in Iraq the looting apparently goes on; aerial photos show historic sites dotted with telltale holes dug by looters.
"They look like Swiss cheese," Zettler says.
The University of Pennsylvania's bronze items, on the other hand, were excavated legally and carefully cataloged, he says. Back when the young nation of Iraq was under British influence, archaeologists from the University of Pennsylvania and the British Museum spent parts of 12 years in the desert, unearthing the riches of the long-dead civilization.
Everything they found was divided between Iraq and the two museums.
Occupied for almost 5,000 years, and gone by 500 B.C., Ur was a prominent political and economic center as well as a sacred city of the moon god, Nanna. The Bible identifies it as the home of Abraham.
The University of Pennsylvania's share from Ur is the largest such collection in the United States. It totals 7,100 items, including jewelry of gold, silver and semiprecious lapis lazuli that do not need treatment, for now.
Some of the stuff, including bronze pieces that were in relatively good shape, have been on a national tour and only recently came back to Philadelphia.
But the most fragile bronzes never left their home on South Street. They need work.
And so as custodians of history, the museum staff does what it can to preserve it - one piece at a time.
Ancient bronze has three principal enemies: oxygen, humidity and chlorides - salts from organic matter or the earth in which it was buried.
"The oxygen, we can't do anything about," quips Greene, the senior conservator.
Humidity is another matter. The university's renowned museum is in an old building with imperfect climate control, but staffers place dessicants in the storage cabinets.
Otherwise, there would be trouble. The copper in the artifacts has reacted with the chlorides in the soil to produce cuprous chloride. Add moisture and you get hydrochloric acid, which feeds a corrosive cycle known as bronze disease.
Conservators also treat items with a solution of benzotriazole, a chemical that combines with the chloride ions and immobilizes them, slowing deterioration.
Some get a surface treatment; some get dunked.
Last week, Lawson placed a bronze projectile - perhaps a spear tip from a forgotten battle - in a beaker of the solution. She sealed the beaker inside a larger container and turned on a small vacuum pump.
This forced air to bubble out the pores of the artifact so the corrosion retardant could take its place.
"You wouldn't believe how much air is in an object," Lawson says.
Once removed from their bath, some objects are also brushed with protective lacquer or other coatings, including one first developed for industrial use by Philadelphia chemical maker Rohm & Haas.
The goal is to treat objects before they reach a light green, almost a bright jade hue. By that point, some of the corroded metal begins to flake away.
The project, funded in part by the federal Institute of Museum and Library Services, involves conserving 786 items of copper, bronze and other copper alloys, as well as 21 iron objects.
The iron items - spear points, arrowheads and a small sword - are handled differently. They are cleaned, then brushed with a tannic-acid solution. This reacts with the metal to form a corrosion-resistant compound, called ferric tannate, on the surface.
As the pieces lie on the table awaiting treatment, it's not hard to imagine them as they once were in the hands of the ancients. The knife blade Lawson worked on still has two rivets on one side, a long-ago means of securing the blade to a handle of wood or bone.
Nearby, a longish spear tip looks as if it could still inflict damage in the hands of a tunic-clad soldier, if it were lashed once again to the end of a pole.
"That's probably not for throwing, but poking," says Zettler. "Moving prisoners along."
After treatment, the items will be rehoused in padded polystyrene boxes or in custom storage mounts, as needed.
Rescuing the metal pieces is not the museum's only recent work with Mesopotamian items.
With the help of a separate federal grant, Lawson also treated a series of unusual clay coffins that were unearthed during the university's first dig outside the United States, in 1889.
Some are called "slipper" coffins, with an opening at one end that must have been used to slip the body inside, feet first.
About 2,000 years old, they were dug up from burial grounds in the city of Nippur and brought to Philadelphia by steamship.
For years, they had been largely forgotten in a damp sub-basement in the museum, and had begun to fall apart. So Lawson had to assume the role of jigsaw puzzler, fitting the pieces back together with adhesives.
"These are the only examples of these kinds of things that exist in this country," says Zettler, who hopes to display some soon.
The bronze conservation effort, meanwhile, will last until summer.
The conservators have completed 600 of the 807 items so far, Lawson says - "if you count every little nail, etc., which of course we do."
Then it's on to the next, yet-to-be-determined project.
Museum officials are discussing more upgrades in their storage facilities, which might include new cabinets and better humidity control. And some portion of the museum's collection - close to one million items - is always in need of care.
For those whose job is to keep history alive, Greene says, the pursuit never ends.
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(c) 2007, The Philadelphia Inquirer. Distributed by Mclatchy-Tribune News Service.
