corrosion

[Robert]

I don't know much about early U.S. copper, but I do seem to see a lot of early large cents with heavy pitting/ corrosion.

Does anyone know the source/ reason for so much corrosion on these particular coins?

[coppercoins]

I believe it came from impurities in the copper. Don't quote me on that...LOL!

[Bob P]

Chuck has got it right on Robert. The processes for making planchets those days wasn't much different than what they are today, but thier smelting techniques weren't the best. Many of the early coppers corroded easily, many times form the inside out. Impurites in the copper was a primary factor. and many times gas bubbles were trapped in the metal making the surface of the coin much more brittle. Any hit to the coin may have disturbed or broken the outermost surfaces leading to pitting and corrosion.

Bob P

[GarryN]

Planchets were sent by ship from England and many were corroded before they were coined. That is the cause of corrosion on the 1799, for example.

[smed]

Don't forget rusted dies... I don't know of any in particular, but I remember reading somewhere about particular issues being struck from rusted dies and that causing pitting on those coins...

[coppercoins]

Smed has a point...there were many rusted dies used on those old screw presses - not like these days where a die can punch out a million coins in a day and be worn out of use before even surface rust would have a chance to set in - those dies back then were used for weeks to mint their measly 5,000 or so coins before being replaced, and there was no environment control in the old mint...other than 'windows open' - 'windows shut' - 'fireplace lit' - 'fireplace unlit'

[Mark]

Presumably mint officials stored the dies in grease when they had to shut down the mint for a more extended period of time, eg, to run from yellow fever. But I presume that the grease wasn't a wonderful solution when it came to avoiding rust, so I guess that the stored dies probably had a tendency to rust.

Mark