Rescue Project “Endeavour
Cannon”
By Carmen Welss
|
|
Rescue Project “Endeavour
Cannon” |
|
| It was high tide at eleven o'clock on the night of 11 June 1770 when Captain Cook’s barque Endeavour ran aground on an unseen shoal on the Great Barrier Reef.
The only way to refloat the Endeavour was to lighten the ship as much as possible before the next high tide, and six of the Endeavour’s 10 cannon were heaved overboard. After the ravages of nearly 200 years under the sea, maritime archaeologists brought them back to the surface. To preserve the cannon, they had to be submerged once again – this time in an electrolytic bath. After conservation treatment, one of them became part of the display at Captain Cook’s landing site at Kurnell. The cannon’s Achilles Tendon The original electrolytic reduction treatment, which was applied in the 1970s, seemed to have stopped the ravages of time, until about twenty years later when the cannon’s Achilles tendon was discovered. As legend has it, Achilles’ mother tried to make him immortal by dipping him in the river Styx, but she held him by the heel, which never got wet, and there it was that the fatal arrow hit him. The cannon, while lying in its electrolytic bath, had rested on two supports. Corrosive salts were trapped at these points continuing to cause corrosion activity. The need to move or rotate the cannon to expose all surfaces to the solution had been overlooked during the treatment process. To make matters worse, electrolysis cannot be repeated as the surfaces are very likely to spall off. Search for a treatment To save the cannon, the Foundation sent it on yet another journey this time from Kurnell to Western Australia. As the conservator of Iron artefacts at the WA Museum, Jon Carpenter is a specialist in cannon preservation. “Cannon recovered from the sea usually require a minimum of three years conservation treatment to remove corrosive salts,” he explains. Any re-treatment method must only be carefully applied to the two problem areas of the cannon.
The first attempt to stop the corrosion process was to vaporise the chemical diaminoethane in a steam bath. The vapour condensed on the corroding areas of the cannon, and while reverting to its liquid state it extracted corrosive salts (chlorides). Establishing a safe operating method proved difficult and since the chemical posed too great a health risk an alternative treatment had to be developed (diaminoethane can permeate intact skin and cause major temporary or permanent injury). Eventually, scientists from the University of Western Australia and museum research staff found a potential solution in the amino acid complex EDTA. When EDTA (ethylene-diamine-tetra-acetic acid) comes in contact with certain substances, it combines with them and removes them. This process, applied to the corroded areas of the cannon, is efficient, but it takes time, in this case an anticipated period of two or three months for all chloride to be extracted. Last Destination Kurnell The cannon's treatment and restoration should be finished by September when it will again be displayed at Captain Cook’s landing site Kurnell. Jon Carpenter gives some advice on how to maintain the restored glory, “The cannon should be exhibited in a controlled environment situation, not located outside. Relative Humidity should be less than 45%. Since the graphitised surface of the cannon is vulnerable to damage it is recommended that it not be touched or handled excessively.” In summing up his thoughts Jon says, “It is both challenging, and rewarding to have the opportunity to conserve an historically significant artefact, one of national and international importance. It could have been just another cannon but this cannon came from Cook’s Endeavour.” This
project is possible thanks to generous sponsorship by Caltex Refineries
(NSW) Pty Ltd. |
