1985 D Lincoln Cent Error? Or Acid?

. Not acid. The copper plating got broken some how and now the zinc core is being espoused to the air causing zinc rot.
John1

It's known as zinc rot which is self explanatory.

to the CCF!

Regardless if listed in a book or not, zinc rot IS a real thing, and it IS real deterioration of the zinc core, and it IS detrimental to ALL post '82 cents. Countless examples of zinc rot can be found through out pages here on CCF.

This coin posted was damaged not by acid (acid leaves its own traces), but how it happened is not important, as damage is damage however done. Zinc rot HAS set in to the exposed zinc core and that spells DOOM for this cent. Once started, there is no reversal.

I cited a first rate reference. It outranks you as an authority in that field.

Tossing it out as meaningless? That sounds just like someone who has posted a PMD coin that they believe is a valuable error, and after consulting authoritative references like error-ref.com, saying they don't care and that they will stick with what they want to believe.

If I had written papers for my PhD thesis—which covered some aspects of corrosion prevention—that way, my committee would have eaten me for lunch.

Nope.

In grade school at the time.

Plus, zinc corrodes easily. Copper makes an excellent cathode. Tiny hole in the copper plating means that there is a huge cathode area relative to the anode area. It is an example of an extremely destructive galvanic couple (why you try to avoid connecting dissimilar metals in corrode environments). The thing is prone to fail because of its design.

The historical origin of the term "zinc rot" seems to be old, and related to intergranular corrosion of die cast. One reference mentioned lead or other impurities. I would not think we would allow much lead in our one cent planchets, so maybe this type of corrosion is not so important in our cents.

Why is it important to use more exact language? There are multiple reasons, but for one, if you understand how and why a coin is degrading, you might have a chance of slowing or stopping the process. I am still learning about some of the details about corrosion in coinage metals. One of the areas that I really want to learn more about is what has been called "bronze disease" in some other disciplines. I once saw that BadThad threatened to write a book on it. I've been looking. And while that term is more broadly used, it does seem that once again, a word that implies a biological cause generates some confusion.

If you have some science or engineering based references discussing zinc rot, please send them to me. I have looked for corrosion studies related to coins, but without much success regarding modern coinage. In fact, one promising paper I found on denickelification of cupronickel alloys specifically and deliberately excluded coinage metals. As I have joked before, apparently there's not enough money in this topic for the corrosion scientists and engineers.

Another reason to think about what we say? When some new poster thinks they have a missing clad coin, for example, what they are told is a "stain" sometimes is probably a copper enriched surface. It looks to them like copper on top, because it is. We often can rule out the missing clad hypothesis for numerous other factors, but they haven't seen enough coins or read enough to accept what we do. If they struggle to believe us, you have to have a bit of patience sometimes, because yes, that "stain" looks like copper to them because it is. I could see where a newb would think that it is us veterans (I am using that term loosely by including myself, but I don't recall questioning PMD coins even when I was 14. Usually, that seemed easy to identify, to me.) who are in denial if we aren't careful when dismissing something as a "stain."