1733 Spanish Galleon Trail: Explore the Spanish Plate Fleet disaster of 1733.

Why are all the cannons and anchors falling apart?

A badly corroded cannon from the 1733 fleet

As you drive along the Overseas Highway through the Keys, look for iron cannons and anchors in front of restaurants, strip malls, marinas, and in roadside parks. These artifacts were salvaged from 1733 fleet wrecks and other ships before the consequences of removing waterlogged objects from the marine environment were realized. If you stop to inspect the artifacts you’ll see the effects of long-term corrosion. Large pieces of the metal are literally peeling off and rusty flakes and chunks pile up under the remains of the cannons and anchors. Eventually, they will crumble away to nothing. The reason for this deterioration is lack of proper conservation when the object was taken from the sea.

Iron and other metals react with seawater forming, over many years, a hard covering of corrosion products called concretion that often includes sand, shell, and coral from the surrounding environment. If the object is taken from the water and not conserved to remove salts and stop the corrosion process, it will quickly begin to fall apart. Ceramic, glass, and organic materials such as leather, rope, wood, and bone also require conservation to remove absorbed salts, to preserve their appearance, and to stabilize for curation and exhibition.

Conservation methods depend on the type of artifact and include soaking in fresh water and treatments with various chemicals to prevent warping, crumbling, and shrinking. Metal artifacts often are treated by electrolytic reduction to remove concretions and restore the metal. In the case of large iron objects such as cannons and anchors, conservation treatment can take years and become extremely costly. For these reasons, archaeologists often prefer to leave cannons and anchors on shipwreck sites. Over time the artifacts reach a state of equilibrium with their environment and, if not disturbed, will last for centuries. Wouldn't you rather see a shipwreck looking as it did when it wrecked with its cannons in place instead of rotting on the roadside?