Bronze disease is a big headache for archeologists, historians, and museum curators. Bronze is an alloy made from copper and tin. It's one of the oldest alloys known to humans, and as a result, lots of ancient artefacts are made from bronze.

Because the corrosion is irreversible, it means a lot of ancient artefacts have been destroyed by bronze disease, and many more need to be carefully preserved to prevent damage.

Bronze disease is caused by a combination of water, atmospheric oxygen, and chloride. These three things make an environment which will ultimately wreck any copper objects.

It works in a cyclic process:
• Oxygen oxidises the copper
• Copper forms copper (I) chloride CuCl
• That CuCl reacts with water, making a mixture of copper (II) chloride CuCl2, copper hydroxide Cu(OH)2, and hydrochloric acid

In air, the copper continues to oxidise, and form more hydrochloric acid, and so the process continues.

This means that big copper-based objects near the sea, like the Statue of Liberty are probably doomed.

The only way to stop the process is to remove one of the three things, chloride, water, or oxygen.

Keeping things in dry conditions will pause the process, but just a little moisture can set it off again.

Removing the chloride is more difficult. If you're lucky, it can be polished away. If you're less lucky, you need to use chemical treatments to remove it. And those aren't always possible