This cannon connects us to the Endeavour crew's worst moment on Cook's first voyage of discovery.
At eleven o'clock on the night of 11 June 1770, with the tide high, the Endeavour ran onto a coral reef and stuck fast. It was the worst fear of the crew on a lone ship, sailing in unknown waters half a world away from home. For weeks, James Cook had been painstakingly manoeuvring north along the eastern coast of Australia in a labyrinth of islands and sandy shoals. Little did he know that he was travelling into a funnel formed by the coast on one side and the Great Barrier Reef to the east. It was only a matter of time before the ship would come up against a ripping spur of coral.
This cannon was one of six that were heaved overboard to lighten the ship, along with the gun carriages, some ship's ballast, barrels, and rotting stores - about fifty tonnes in all. The hope was that the ship would float off the reef at the next high tide. She didn't, and at next low tide she heeled over and started taking on water. But with everybody on board, including the gentlemen naturalists, manning the pumps for fifteen-minute turns, she floated off on the next high tide. After being beached for temporary repairs, the Endeavour managed to sail on to Java for proper attention.
Nearly two hundred years later, what had been discarded was wanted again. An American team went on a search for the Endeavour's jetsam. Using a magnetometer, they found significant metal objects on Endeavour Reef, as the disaster spot was later named, four to six metres under water. Six cannons, as well as metal and stone ballast, were recovered from the site.
Coral growing healthily for 199 years had laid a metre-thick cover over the cannons. The bulk of the growth was blasted off and the still coral-encrusted cannons were prised from the reef. They emerged into the air, all set to corrode rapidly. The Australian government stepped in to preserve this prized 'rubbish' from Cook's exploration.
The job of cleaning and conserving the cannons was taken on by the Australian Defence Scientific Service. First most of the coral encrustation was chipped away. About 90-140 kilograms of growth was removed from each cannon (each weighed over 500 kilograms when it originally went overboard). In fact, coral was found to have protected the cannons from rapidly corroding under water. Wherever the coral had grown, the surface was remarkably intact.
The cannons were then cleaned with fresh water, and stored in baths of a weak solution of caustic soda (2 per cent sodium hydroxide) to keep the metal stable.
The next stage was to remove the corrosive salts that had permeated the surface layers of the metal after two centuries under water. This was done by electrolysis - weeks of immersion in a bath of weak caustic soda, with an electric current flowing through the objects in the solution. Every two weeks, the cannons would be taken out and scrubbed in fresh water to shift the particles of coral still clinging to the surface.
The cannons were given prolonged washings with distilled water to remove the last traces of the salts. They were then dried using infra-red heat. As a last step they were given a protective coating of a special wax.
The Australian Government gave this cannon to New Zealand to mark the bicentenary of Cook's first visit here. One of the other five went to the Philadelphia Academy of Natural Sciences, which had backed the expedition to locate the cannons. One went to the National Maritime Museum in Greenwich, England. The remaining three went to museums in Canberra, New South Wales, and Queensland.
Text originally published in Tai Awatea, Te Papa's onfloor multimedia database (1998)