Conserving Metals Heritage in Aotearoa New Zealand – Australasian Corrosion Association

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The 2022 ACA NZ Branch AGM was held in New Plymouth in April, followed by a technical presentation by Susanne Rawson, Taranaki Division Committee Member, Heritage Preservation & Field Support Solutions. Titled Heritage Conservation of Metals in Aotearoa New Zealand: Case Studies, the conference took place in person and streamed online via Zoom.

Susanne’s presentation covered some of the interesting projects she has managed and been involved in throughout her career. These include HL Hunley, which in 1864 became the first submarine to sink an enemy ship. Raised from the seabed in 2000, the Hunley has been inspected and cleaned for preservation and is kept in a water tank.

The USS Monitor was one of the first ironclad warships and one of the first to feature a rotating turret. In 2002, the turret and other parts of the monitor were lifted from the seabed. The turret is kept in a water tank with cathodic protection applied to it. The restorers had wanted to remove some of the 8 layers of iron plates to clean up salt and other corrosives that had seeped in, but did not, fearing that the plates would return to their original shape.

The Daring was wrecked near the southern head of Kaipara Harbor in 1865 during a storm. After its discovery in quicksand in 2017, the ship was removed and retained by a charitable trust and is now in Mangawhai, where it was originally built (see more details here). Many challenges are taken up to preserve what remains. The Daring has a kauri hull, originally clad in Muntz metal (a copper/zinc alloy) to protect against earthworms. The hull of the kauri turned out to be in relatively good condition, the structure of the pohutakawa is not so good. Conservators are concerned about the leaching of iron oxide into the wood and the catalysis of sulfur into sulfuric acid. The vessel is kept damp to preserve its wooden structure while decisions are made on permanent preservation. Susanne asked for the public’s opinion on options to preserve the ship.

In Antarctica, Susanne worked on Captain Scott’s hut and Shackleton’s Cape Royds huts, which being near the shore are affected by chlorides, and preservation is made difficult due to remoteness.

In New Zealand, Susanne has also worked on the preservation of cannons, including one at the Founders Heritage Park in Nelson, believed to be Nelson’s old harbor cannon. Its conservation has been hampered by uncertainties about its history. An older resident remembers it as the cannon in time, and also recalls that children were allowed to stuff it with rags and fire it – one group got into trouble for adding rocks and breaking several windows nearby . Susanne led a discussion on the options for removing the existing, non-original coating and replacing it with a suitable permanent coating.

Event pictures

Submitted by Mark Sigley

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