Plating Surface Corrugation

well it would appear that is happening now, Chase.

Thanks for this question! You have forced me to realize the inadequacy of my speculation!

I have found very little help referencing the copper plating interacting with the zinc alloy substrate. I do know that the thinking and justification for including a small amount of copper in the zinc alloy (ALLOY 190: COMPOSITION (% by Weight) Lead = 0.005 max; Iron = 0.010 max; Cadmium = 0.005 max; Copper = 0.7 to 0.9; Zinc = Balance) was to facilitate bonding with the copper plating.

As far as the ridges and valleys being oriented in approximately the same direction on each side, the following explanation has possibilities, although I have not found any research experiments that directly support the hypothesis:

In addition to crystal behavior at the atomic level, Current Density and Electrolyte Flow influence the direction of the formation of the ridges and valleys of a corrugated surface.

A barrel plating process is used and barrel rotation is likely the key factor supporting the same direction ridge/valley orientation on both sides.

-- During barrel electroplating, current density varies (current density variation significantly impacts coating quality, deposition rate, and microstructure) and the electrolyte flow pattern is driven by the rotation of the barrel.

-- In addition, the tumbling action of a metal disc in the barrel plating bath is most likely to be end over end.

This combination of factors is likely a contributing cause for the ridges and valleys on both sides of the planchet being oriented in approximately the same direction.

I'm glad to see this posted here for the continued information. It seems like this "corrugation" may be easily mistaken for roller lines.

On a related note, do you know of anyone confirming that they use an upset mill to form the proto-rim? I can't remember hearing of anyone being allowed to see their production process.
I've always wondered if the producer of the 1c planchets (Artazn LLC) has produced the zinc planchets in a different manner than the mint use to produce the copper planchets.
Could they be striking the blanks with "forming" dies that could contour the surface allow copper plating to build up thicker in certain areas?

Also, Can you share any info on how they solved the problem of split plating that use to be so prevalent on early zinc cents?

Thanks for all your efforts on behalf of all numismatists.

There are two primary areas still to be addressed. One is the applicability of studies (as discussed in the paper) of copper deposition at the crystalline level to the corrugation features easily and commonly seen on many CPZ cents.

The other is the mechanism by which the ridges and valleys are oriented in approximately the same direction on both sides of the planchet/coin.

In addition to crystal behavior at the atomic level Current Density and Electrolyte Flow influence the formation, direction and orientation of the ridges and valleys of a corrugated surface.

In research carried out by the Bureau of Mines to develop new technology for electrorefining metals, the hydrodynamics of electrolyte flow were studied:

"The cathode deposits are relatively smooth but with striations or grooves running parallel to the electrolyte flow. Many of the striations were continuous along the entire length of the cathodes. Their origin is believed to reflect the hydrodynamic flow conditions close to the surface. It appears that either a ridge or groove, once initiated at the front edge of the cathode, propagates along the entire length."

(https://www.911metallurgist.com/blo...ing-copper/)
{In barrel electroplating, the object being plated acts as the cathode}
[This experiment uses multichannel cells which are not utilized in barrel plating. I am assuming, however, that similar results arise from electrolyte flow patterns produced by barrel rotation.]

A barrel plating process is used by the supplier of Cent Ready-to-strike (RTS) planchets for the US Mint. Barrel rotation is likely a key factor contributing to the formation of ridges and valleys and in their alignment in the same direction on both sides of the planchet/coin.

Current density varies, resulting in thicknesses that vary.

An electrolyte flow pattern is driven by the rotation of the barrel, resulting in striations or grooves running parallel to the electrolyte flow.

The result of these dynamics builds on the crystal orientation patterns developed at the atomic level.

The tumbling action of a metal disc in the barrel plating bath, as the barrel rotates, is most likely to be end over end, resulting in electrolyte flow patterns being in approximately the same orientation on both sides of the planchet.

I am unable to confirm the upsetting method used, however I think from the standpoint of production efficiency, an upsetting mill would be the preferred option.

We know that plating thickness does vary on individual pieces and probably is significantly thicker on proof coins (I will post a paper dealing with proof coin plating), so it is not necessary to posit an irregular surface for the zinc alloy substrate.

I have found minimal evidence to suggest plating irregularities are due to characteristics of the zinc alloy substrate outside of the possibility of an improper alloy mix contributing to a lack of bonding. A small amount of copper is added to the alloy to facilitate bonding and if there happens to be an improper mix, then conceivably separation may occur. I think the odds of an improper mix are inconsequential since there is such a tiny amount of copper included. ZINC ALLOY 190: COMPOSITION (% by Weight) Lead = 0.005 max; Iron = 0.010 max; Cadmium = 0.005 max; Copper = 0.7 to 0.9; Zinc = Balance.

That is really good insight into one of the criticisms of the plating.

There is another step in the process used to make the plated planchets. It's apparently an ARTAZN trade secret as to how it is done, but the plating is double thickness on the edge. Whatever the process, this step may be worth considering in the analysis. There is also some indication that the plating thickness may have been increased after the date of the following report. If so, the date of the coin may be an additional factor to consider. Here is the report information.

The Final Report, Alternative Metals Study (for circulating coinage), submitted to the US Mint by Concurrent Technologies Corporation under Contract Number TM-HQ-11-C-0049, 2012.

The double plating on the edge is mentioned in other materials. There is a mint report on it somewhere, and the Jarden/ARTAZN website mentioned it at one time. I can try to search for my materials on this. It is the edge itself, and not the surface near the rim, that has double plating.

I thought of two more things to consider. First, unlike other planchets, the mint does not anneal the zinc cent planchets before striking. Annealing is done by ARTAZN, but when and how in their process seems to be another mystery. Second, some of the zinc cents were in the toxic soup of the flooding following Hurricanes Katrina and Harvey. Some of these survived and were acid cleaned to return them to circulation. Broze cents that went through this cleaning have a readily identifiable orange tinge, even in circulation today. I haven't seen enough of the surviving zinc cents to have a good feel for what the treatment did to them.