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Do old coins corrode brass?

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This may be a silly question...but do old coins corrode brass?
I collect old coins that turn up in my every day change.
I usually scan the dates and collect anything older than 1970 or anything unusual and squirrel them away in my safe...eventually.

However before I put it in my safe, I usually throw the coins in a tiny little tupperware I keep in my night stand, which is also where I keep two .38 special speed loaders ready to go.
Last night I noticed the rounds that were sitting on top of my old coins were starting to get very discolored and a tiny bit corroded.
Even the hollow point bullets were showing signs of discoloration. Very strange.

I spent the better part of last night cleaning all the rounds indavidually with "Never Dull" and they cleaned right up...but it got me wondering if it was the coins that were causing the brass to react that way. Mostly pennies and Bicentenial or old Quarters and such.

Has anyone ever seen such a thing?
I started poking around the internet in an effort to see if this is a common thing, but I couldn't find anything
I'm going to find another temporary place to store my coins rather than next to my speed loaders to see if the problem goes away.
Anyone else seen this happen?
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18 Posts
Discussion Starter · #3 ·
I posted this on another forum and got a very informative and helpful answer...

The term for it is Galvanic Corrosion, the layman's version is "Dissimilar Metals Corrosion".

It's not the coins, per se, it's the nickel and other non-brass metals IN the coins, along with residual moisture from your sweat from your pocket, sealed up in a container where it cannot evaporate. Contact between the coin and the cartridge sets up an electrical current like a tiny battery (moisture has to be present, but liquid water is not needed), this sets up the oxidation (corrosion) of the refined metals used in the cartridges. The coins take damage too, but between 2 metals one always takes worse damage in the equation.

This is why Zinc blocks are used in freshwater boats as sacrificial corrosion points (Magnesium in salt water). They corrode away in place of the brass propellers and rudders, stainless steel props and shafts, Aluminum impellers, housings and manifolds, iron engines..... The blocks are cheap, and easy to change periodically.

Moderator Emeritus
27,619 Posts
You are correct on the galvanic corrosion, when I was in aircraft maintenance they were just starting to use aluminum wiring on aircraft, using copper connectors with aluminum wire caused corrosion resulting in overheated connections, burned wiring and sometimes connections just breaking apart. The problem was cured by using grease in the connections to block the moisture.
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