Many objects raised from the wreck of Invincible have a very strong smell. This isn’t because they have started to stink over time. The rope still smells of the tar used to waterproof it in 1758 and the gun powder still has that rotten egg, sulphuric smell. How can smells survive over 260 years?
Protected under the seabed
Under the seabed, it is an anaerobic environment – that means there is no oxygen. Bacteria slowly breaks down anything organic (things that once grew, like wood, leather or paper) and it needs oxygen to function.
Other marine creatures also need oxygen to live, and so couldn’t munch away at Invincible’s timbers. Thanks to this anaerobic environment, the objects on Invincible are so well-preserved that even some of the original smells survive.
The seabed is like a tin of beans
Imagine the environment under the seabed as a sealed tin of baked beans. While it is sealed no oxygen can get in and the beans stay fresh. Once you open the tin, the baked beans will start to dry out and then go off (unless you eat them).
The same is true for objects from Invincible. Once you raise them and expose them to oxygen the objects start to dry out and crumble. Bacteria also become active again and will begin to slowly rot the objects. This is why it’s important to conserve such well-preserved things from Invincible. The archaeologists immediately place each object into fresh water tanks to start the conservation process, keeping things nice and wet.
It’s not all good news
Not everything in Invincible has survived well. Where her timbers have been exposed to the sea water, marine borers like shipworm and gribble have been eating away at her. Shipworm burrow deep into timbers and gribble destroy the surface layers. The result is timber that crumbles in your hands. This is why it was so important to excavate and record the wreck, before it is lost forever.
Iron and seawater don’t mix
Iron – and, in fact, most metal objects – don’t survive well in salty seawater. The salt is a catalyst, producing a chemical reaction that forms a ‘concretion’ around the object. Larger iron objects like the shot for Invincible’s guns can still be found inside the concretion. But the chemical reaction slowly destroys the iron and so smaller objects can disappear completely, leaving a ghostly shape where they once lay inside the concretion.