Searching For Black Beard

Science World, March 8, 1999 by Laura Allen

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.