SEARCHING FOR BLACK BEARD.

A ship's watery off North Carolina coast. What clues link the wreck to a notorious pirate?

Head for land!" Blackbeard the pirate bellows from the deck of his wooden ship, the ribbons braided into his bushy beard rippling in the wind. He laughs greedily--and why shouldn't he? In one week of this summer in 1718, Blackbeard and his crew of 300 thugs have ambushed nine merchant ships, plundering their cargo of precious gold and silver.

Then, suddenly, Blackbeard's ship screeches to a halt, its timbers shivering. "We've run aground!" hollers one of the pirate crew. The ship is mired on a shallow sandbar just outside Beaufort Inlet, North Carolina. Feverishly, Blackbeard loads his favored men and their loot onto a smaller boat in his fleet. They sail off as the stranded pirate ship, the Queen Anne's Revenge, slowly tips, floods, and sinks into oblivion.

Fast-forward to a November day in 1996. Scuba-diving scientists comb the inlet's seafloor, hoping to detect any sign of Blackbeard's ship. After several hours they spy a large mound of sand with protruding objects. Swimming closer, they're astonished to catch sight of the remains of rusty cannons and anchors. Could these sunken relics once have belonged to the Queen Anne's Revenge?

MYSTERY WRECK

In the last two years, scientists have unearthed hundreds of artifacts (objects used by humans long ago) from the mystery wreck, including metal plates, a bell, a syringe, weapons--even gold! Treasures like these give underwater archaeologists, scientists who study the materials of past human cultures, evidence of long-gone seafarers' lives.

Armed with such high-tech wizardry as computerized mini-submarines and improved magnetometers (sensitive metal detectors), scientists are discovering and probing shipwrecks far more easily than they could have even five years ago.

Could the shallow-water discovery in North Carolina reveal new clues about Blackbeard? "We're still hunting for solid proof that the ship is Blackbeard's," says Richard Lawrence, the project's head archaeologist. Read on to weigh the evidence about one of history's legendary mystery wrecks.

FLAKY FIND

FACT: When it sank, the Queen Anne's Revenge was hauling nearly 9 kilograms (20 lbs) of gold dust--tiny flakes that can be melted into jewelry or gold bars.

CLUE: Gold flakes were found scattered at the wreck site.

Even in murky water, divers easily spotted gold specks. That's because gold is nature's only metal that stays shiny underwater--it doesn't corrode, or break down. Corrosion occurs when water, salt, and oxygen transform a metal's surface by turning it into a new substance--usually a dark, dull, or crumbly one (see Corrosion at Work, left).

The process of changing one material into another material is called a chemical reaction or chemical change. Just take a look at a rusty car fender. Oxygen molecules in the air react with iron molecules in the fender to produce rust, a type of corrosion. Since gold doesn't chemically react with water, salt, or oxygen, it doesn't corrode.

The gold flakes may have been part of the loot Blackbeard left behind in his rush. But that doesn't prove the mystery wreck is the Queen Anne's Revenge. Many merchant ships hauled gold dust in the early 18th century.

DATING SERVICE

FACT: The Queen Anne's Revenge sank in June 1718.

CLUE: Many artifacts from the mystery wreck date to the early 1700s.

Dating some artifacts is as easy as carefully cleaning off corrosion (see sidebar, p. 19). "The most datable artifact was a corroded brass bell," says Lawrence. After cleaning, the date "1709" could be seen clearly etched in the metal. Archaeologists also uncovered plates made of pewter, a silver-colored metal, marked with the name "George Hammond." Hammond was an English craftsman who fashioned his plates between 1693 and 1709.

So far, divers haven't located any artifacts dated after 1718. If they do, it would be undeniable proof the mystery wreck is not the Queen Anne's Revenge.

BIG GUNS

FACT: The Queen Anne's Revenge was loaded with about 22 cannons.

CLUE: So far, 18 cannons have been found at the mystery wreck site.

Historical records show that 12 ships sank in the inlet during the 1700s, Lawrence explains. Of these, Blackbeard's was the only ship known to have had more than 18 cannons.

Like most shipwreck artifacts, the cannons were found covered with a grayish concretion, an inch-thick, rock-hard crust of sand, salt, and calcium carbonate, a chemical compound found in seashells. When two different metals--like pewter and iron--lie near each other underwater, a tiny current of electricity runs between them. Just as static electricity makes your shirt cling to your body, the electricity between metals attracts tiny particles of calcium carbonate dissolved in seawater.

The 18 cannons don't offer conclusive proof that the wreck is the Queen Anne's Revenge. If divers find four more cannons, however, the complete set would definitely further Lawrence's case.

SOLVING THE MYSTERY

Clues are tantalizing, but Lawrence warns that only an artifact directly linking the ship to Blackbeard himself would make for a positive ID. Blackbeard stole the Queen Anne's Revenge from the French in 1717. Previously, it had been called the Concorde. So a pewter plate etched with the name of the Concorde's captain would be a dead giveaway. Blackbeard probably wouldn't have wasted time or money redecorating his ship, says Lawrence.

His team plans to dive again this summer and fall, searching for final proof: "The best information we have about pirates could still be lying at the bottom of the sea."

CORROSION AT WORK

A diver peers through the porthole of a rusty, underwater iron hull. What makes iron rust in water? It's a chemical reaction.

Every chemical reaction begins with a certain number of atoms (tiny particles) and molecules (combinations of atoms). The atoms and molecules react (combine in a new arrangement) to make entirely new matierials. Read the steps below for more:

Chemical equation for rust:

1. Iron rusts only when water and oxygen are present. In the ocean, oxygen is dissolved in the water.

2. The oxygen atoms bond (combine) with the iron, creating hydrated iron oxide, or rust.

4Fe + [3O.sub.2] + [H.sub.2]O = [2Fe.sub.2][O.sub.3] [multiplied by] [H.sub.2]O 4 atoms of iron + 3 molecules of oxygen + 1 molecule of water = 2 molecules of iron oxide

Excavating a shipwreck

It may take years to completely excavate the sunken ship in Beaufort Inlet. Here's how archaeologists are doing it.

1 TAKE A DIVE 

Archaeologists don scuba gear and grab shovels and buckets to excavate the wreck, which is just 7 meters (23 ft) below the sea surface.

2 RECORD THE SITE

After laying a grid of ropes over the site, scientists sketch and map the location of each artifact in the grid. Having this record provides clues about which artifacts were cargo and which might have personally belonged to the pirates.

3 PRAISE THE ARTIFACTS

The divers suck away sand using underwater "vacuums" and swim most artifacts to a boat. Heavy objects like cannons need a lift with cranes or special balloons. First, divers haul an empty balloon down to the site. After roping it to the artifact a diver inflates the balloon using an extra scuba tank. Once the total weight of the balloon and cannon is less than an equal amount of seawater, the cannon becomes buoyant, or floats.

4 CLEAN THE ARTIFACTS

Odd-shaped crusty coverings or concretions are X-rayed first to discover what's inside. Using the X-ray image as a guide, archaeologists called conservators gently chip away the crust wit hammers and chisels. Some light concretions on delicate objects can be dissolved by an acid soak.

5. PRESERVE THE ARTIFACTS

As iron artifacts dry out, dissolved salt soaked into the iron begins to crystallize, or link together in an orderly arrangement of tiny cubes. This structure takes up more space than salt dissolved in water, so the salt expands. This interior "push" can crack the iron to pieces! So, conservators soak cannons in fresh water for months to wash out the salt. A paint-like coating on the cannon prevents oxygen and water from rusting it further.