"Texas" cents with stripped plating.

[willbrooks]

We are seeing more and more of these cents with stripped plating that have a larger-than-normal diameter. I decided to post a thread about this, hoping for some more input and discussion about this little mystery. After doing some more research and experimentation, I decided I needed to edit this glossary entry as well. I currently surmise that the exposure of the cent to harsh acids, chemicals, and heat during the stripping process is also causing this distortion of the zinc core, rather than it being from mechanical means. If you have any insight on what may be happening here, please discuss. I'd surely like to get Thad's input on this. He surely would have some insight here. Here is how the entry reads now:

Texas Cent: A cent with a larger-than-normal diameter that was intentionally damaged outside the mint. The traditional method is hammering the cent between pieces of (usually) leather. However, another instance of cents with larger-than-normal diameters is now commonly seen on cents that have had their plating removed. Whatever methods are being used to strip the plating, most of which involve exposure to chemicals and heat, are leaving the resulting zinc core thinner with an expanded diameter. I am still trying to investigate exactly how this is happening. Below is an example of one of these stripped cents. Photos courtesy of jallengomez.

[jallengomez]

I don't know. I've been experimenting myself. My original hunch was that it might be possible to heat the cent up so that the zinc core liquified and thus separate the bond between the core and the plating. I did this, and I then hammered the cent between two pieces of cardboard. I definitely ended up with a Texas sized cent, but I couldn't get any separation of the copper plating. I definitely think we can toss out the theory that they are simply cents that have been hammered between a couple of pieces of leather. That doesn't separate the plating. Even if you melt the zinc core first.

[GrumpyEd]

Cleaning up zinc cents (making them spendable) that were from metal detecting some had no plating, some were slightly cupped and some were bigger. To spend them I gave the cupped ones a light whack and they get flat and are bigger than normal.

The only thing unlike most supposed "Texas" cents is that most of them were dark in color but other people might clean up their detector finds with something that fixes the dark color.

When zinc cents are in moisture they're bubbled and pitted and often missing chunks along the edge. The ones that were complete and de-plated were from dry hot sandy places where it looked like the cent had been there long and in most cases right on the surface baking in the sun for years.

Anyway, I think at least some of these are naturally created in that way and it takes certain conditions like hot and mostly dry and some sun and maybe something about minerals or acidity in the dry sandy areas. I'm Arizona, maybe Texas is also a place with the right conditions to make them.

When I noticed how several of my metal detecting zinc cents were de-plated I remembered an old thread on the forum from a guy that kept finding them in his yard. After seeing that some conditions do this, it made me think of that thread and I think he was finding the same thing probably because of the conditions where he was finding them. I didn't take pics because I'm always eager to spend any detecting find coins because they're damaged and not worth saving so I clean em up and spend them on my next shopping trip but the pics in that guys thread look about the same as the ones I'm talking about. See that thread:

http://www.lincolncentforum.com/forum/showthread.php?26197

http://www.lincolncentforum.com/forum/showthread.php?26410

[jfines69]

Will the mad scientist Thanks for the update... It is fun to test out theories... Not only that it can answer lots of questions and create new ones... Could it be that these Texas cents were flattened first then had the plating removed electrically???

[BadThad]

I'm thinking this has something to do with heat and a modification of the metallic matrix, i.e. unintentional alloying. Did you measure the diameter difference with a caliper?

A few things to consider:

1) There is a large difference in the melting points between copper and zinc (1981°F vs 786°F).
2) Also a large difference in the coefficient of thermal expansion between copper and zinc (16.6 mm/mm*K vs 29.7 mm*K).

A typical wood fire burns at around 1100°F, not enough to fully melt and remove the copper, but much higher than zinc's melting point.

Toss this data around in your mind Will and see if you have a theory based on heat and physical properties.

[willbrooks]

Thanks, Thad, There are several tutorials online about how to do this. Many of them involve heating the solution to boiling and leaving the coin in there for a half hour or so. The question is, is this enough heat to cause the zinc core to soften enough or expand and stay that way? I guess I need to try to acquire the needed chemicals and attempt it myself and see what happens, unless Thad wants to try it? You are surely more well-equipped to do it properly. I'll probably end up like my avatar for real!

[BadThad]

cause the zinc core to soften enough or expand and stay that way?

I'm speculating that some impurities get infused into the metallic matrix (maybe even converted to oxides) causing it to permanently expand after cooling.

How much of an increase in the diameter is there or your sample coin? What is the weight difference?

[jfines69]

The impurities coulld explain why there plated LCs with craters in them... Deep gas bubbles that have burst open due to the expansion of the impurities in the zinc???