How do dies rust?

[jtryka]

This may seem like a dumb question, but I've read recent and past posts about coins struck with rusted dies. My question is how did they rust to begin with? If the dies are being used, the metal on metal contact would prevent it from rusting wouldn't it? I am just thinking of a train wheel, which only rusts when a car is sitting for a while out in the rain. What part of the process am I missing that would allow this? Does the mint make up a bunch of dies and leave them out in the back yard for 6 months? Help me out here, because the concept of a rusted die seems so bizarre to me.

[EVillageProwler]

The dies rusted from improper storage. For example, the Philadelphia of the 18th Century was a very humid place. A/C was non-existent then. Natural and man-made disasters, like a malaria outbreak and the fire of 1797, oftentimes prevented the Mint from doing anything and so the dies just sat. And rusted.

 

It is critical to know this when evaluating ED's dated 1797. BB-71, the 10x6 variety, is very frequently seen with annoying signs of die rust. BB-72, the rare 9x7 SmLt variety, is nearly always seen with pocky surfaces due to the poor dies. BB-73, the 9x7 LgLt variety, is the last variety struck with that date. It was certain that BB-73 was struck in 1798, and those specimens come normal looking.

 

Given how lousy the BB-72 looks compared to the other two varieties, and that most think that the three varieties were struck in the order BB listed them, I'd think that BB-72 was also struck in 1798, and due to the availability of the BB-71, perhaps even some of that variety was truck in 1798 as well.

 

Sorry, Jeff, to have turned this into an ED lesson!

 

EVP

 

[jtryka]

That's fine EVP, and I can understand much better how this might happen before the 20th Century, but I have heard this discussed for surprising coins, like Jefferson nickels of the 1930s! That's the part I don't understand, is how could this possibly happen in the 20th century or later?

[BillJones]

The mints have really only been careful with dies and rust probably since the 1940s or so. Back before that it was not unusual for a die to be taken out of service, allowed to rust and perhaps polished before it was put back into service.

 

The 1937-D three legged Buffalo nickel is a prime example of this. The rusted, and before it was used to strike coins, it was polished. They didn't get all the rust as evidenced by the patch that appears on the Indian's neck and the pits under the animal on the reverse, but they did polish off the leg, which created the variety. The 1922 Plain cent with the strong reverse is another example.

[EVillageProwler]

I've always wondered how polishing could account for something like the 3-legged Buff...

 

On the die, the leg is incuse. So, how could polishing remove an incused detail?

 

EVP

 

[BillJones]

Sure it can. I've seen Proof and 1942 and 1952 Lincoln cents with polishing that was so extensive that Lincoln's bowtie was floating in mid air. There are also 18th century large cents (S-77 is one example) where the ends of Ms. Liberty's hair are detached from the rest of her head.

 

Years ago the mint was really hung up on making really bright Proof coins because of collector complaints about the Type I 1936 Proof coins and the dull 1950 Proof coins. That encouraged the mint the polish the dies, sometimes to the point of losing details.