A Pretty High Tech Coin Plating ring...

This. Plating a cent that way will make it look silver, and won't alter its weight enough to measure with home equipment.

I don't know what that plating would do to a Sigma readout, but as I've already said in more than enough other threads, I'm a big Sigma skeptic anyhow.

 

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It seems that you might be mistaking the process. It is the planchets for the coin that zinc blanks that are then electroplated for the outside copper metal layer AND then separately made into the cent coin at the end of the minting process. The copper alloy cents are just minted the old fashion way. Your cent shown as "silver" looks far more like "zinc" plated on a copper alloy cent. Jim

 

Not so much. Zinc is a lot more reactive than copper, and it's tough to find something that will take off the copper without immediately attacking the zinc even more aggressively. In fact, once some of the zinc is exposed, it protects the copper, at the expense of dissolving away even more quickly.

I suppose it can be done. But I don't see any reason to think it's been done to OP's coin.

 

I think the refining process is called the "Mathers and Martin method"
but using nitric or sufuric acid ? will remove the copper and leave the zinc.

There's plenty of YouTube videos of how to do this though not recommended for home playing.

 

There are acids that attack the copper more strongly than the zinc, but they do attack the zinc to some extent as well. That is why cents that have had the copper plating removed (rather than simply having another layer plated over them) have a dull silver gray rough surface with no mint luster.

 

Nitric or sulfuric acid definitely won't leave the zinc.

It looks like the Mathers and Martin method uses sodium polysulfide, which you make from sulfur and lye. I've also seen references to a method using calcium sulfide, which I guess you'd make from lime and sulfur. I may give one of those a try once it cools off. (I'm NOT doing a sulfide reaction indoors.)

 

And that still leaves open the question (from another thread) of whether luster makes it through the copper layer to the zinc. My bet is that it wouldn't; the copper layer starts out 20 microns thick, and I don't think flow lines on a die get that deep. Even if some impression of them did make it through the layer, I'm guessing the resulting luster wouldn't look anything like what we're used to seeing on a directly-struck surface.

 

I know @rickmp stated in 2018 the 20 micron thick which he referenced a comsol.com blog. But all the US MINT documentation reviews thickness tests and their end result selection of 8 micron thick plating.

• The US MInt does reference the Royal Canadian Mint's multi-ply tests of 20 microns but for nickels

• and some nonsense tests for quarters with 5, 8 & 10 micron thick copper

• there were reviews of 25 micron copper over steel

• but I've found no documentation of a 20 micron thick cent.
• but many references of an 8 micron thick plating

• all except for the comsol.com blog

• but the US MINT disregarded security (forging) for the cent coin and seemed to disregard the "bullet points" of the comsol blog.

I did a quick scan of a couple other US MInt docs but couldn't find a 20 micron reference.
so .. I'm just curious where the 20 micron plating came from to correct my knowledge.

 

All I did was a quick Google search, and Comsol was the site that provided the first result. So, busted, I guess. If I get some time and remember the task, I'll look up the actual final percentage composition of the cent, and use that, total weight, density of copper, and surface area to try to calculate a thickness.

 

Perhaps silver nitrate would react with the copper and leave the zinc alone

 

I'm sure if you timed it right you'd get a nice layer of silver as copper displaced it. (Well, probably not a nice layer, more of a mossy layer most likely.) But if it broke through to the zinc, you'd be in galvanic-destruction land, and soon you'd have a copper shell with silver on the outside and zinc-salt sludge on the inside.

Edit: I do have a bottle of silver nitrate; I might even be able to find it...

 

Not sure if the silver would plate out or just form crystals.

 

Yeah, I'm thinking of the "Christmas tree" demo where you hang a copper-wire form in the solution and silver crystals grow on the wires.

 

"When a copper wire is introduced into an aqueous silver nitrate solution, a single replacement reaction occurs. ... At the beginning of the experiment, the pure elemental form of copper (Cu) is oxidised by the silver nitrate solution. This means that it loses electrons and forms copper ions."

 

Your plating weights are incorrect. (OP)
You have a 2.5 coin and .6 of a gram plating to make 3.10.

The plating on a 2.5 zinc coin is closer to 0.06 of a gram.
Making the unplated zinc weight 2.44.
If you were to add that to 2.5, you get 2.56 and not 3.10.

And if the coin was unplated, it would weigh 2.44,
and 2.5 after plating.