Let's talk about bronze disease!
Bronze disease is a type of corrosion which can happen to any object made of bronze, or any other kind of copper containing alloy. It's irreversible and very difficult to stop. It's what causes old pennies to get that green fuzzy coating.
It's also not really a disease, but people used to think it was caused by bacteria.
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
Because bronze disease is a mixture of copper chloride and copper hydroxide, it usually has a mottled green and white colour. The fuzzy look to it is due to the crystals of those two chemicals which form on the surface.
This is also why museums don't like you to touch the exhibits. Even the sweat from your fingers can spread chloride to objects.
I'm posting all this in solidarity with a museum curator in the UK who recently dealt with a shitstorm for pointing out that it would be terrible if bronze statues of racists SOMEHOW got saltwater on them, because then they'd eventually be ruined forever. Which would be terrible. Obviously.
https://www.theartnewspaper.com/news/curator-investigated-for-tweets-on-damaging-bronze-statues
Oh look, it’s an old thread I wrote about bronze disease, and how salt water can permanently destroy bronze statues.
On a TOTALLY UNRELATED note, I’m pretty sure there’s some other guy who people made bronze statues of in America. Can’t remember who. There is no particular reason why I’m mentioning this on October 12th.
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