Plating Split Doubling (Split-Line Doubling)

[jcuve]

Thoughts on Plating Split Doubling (Split-Line Doubling). I have an example below of this phenomena; it is a standard off-centered Lincoln cent where the upper part of Lincoln's portrait has split away similar to some broadstrikes.

I numbered the illustration with three points (1. 2. & 3.), I did this as it seems these points all were present at the same location at the moment of the initial strike before some of the energy of the strike sent parts of the field away. I think it is safe to presume that points 2 & 3 where connected, I am also thinking that point 1 was as well but I am not 100% certain. I think, from just looking at it (and probably not using the correct terminology), that either the speed or physical distance (or a combination of the two) translates into different results with zinc and the copper plating.

I don't know if the correct term is malleability or ductility (or something else altogether) when describing the differences seen between the copper plating and the zinc in this particular situation. It sure looks like the zinc either stretches out more easily or out further at the speed associated with this strike, then when the energy of the strike is not contained within the collar, the copper plating passes a critical point and snaps at what is now a weak point from where the edge of the die had made contact a fraction of a second earlier.

Another idea I have about points 1 & 2 is that the tear occurs near the edge (but not where the die edge made contact), not because it is weaker, rather, as the bend in the coin makes the copper plating more stable and unmovable and the break rips along a line similar to the profile.

I guess what I am looking to know is if it is a case of copper and zinc exhibiting differences of malleability only or if it has something to do with (in part or in whole) the speed of movement of the two metals during the latter phases of the strike.

Below the off-center example are pictures of the Plating Split Doubling where it seems to occur most frequently (the mintmark and outer devices on the reverse of the coin).

[diamond]

The copper plating is quite thin and there are limits to how far it can stretch before it splits. I believe copper is more ductile than zinc, so that wouldn't have anything to do with split-line doubling.

As to why the copper splits on some off-center and broadstruck coins and not others, I can only speculate. It's probably a combination of slight variation in the thickness of the copper plating, variation in ram pressure delivered by the press, and variation in minimum die clearance.

[jcuve]

Mike,

Thanks for responding.

Do you think points 1, 2 & 3 were connected and the split occurred where the die made impact at its edge or is the tear created some random distance from the design (at point 2) and retains the shape of the edge of the design as the bend in the coin holds the copper plating in place. I am starting to think the tear occurs away from the device...

[diamond]

Most splits are close to the design, so I would think the sharply demarcated edge of the incuse design elements in the die face initiate the split. When Lincoln's split-line profile is widely displaced from the die-struck profile, I imagine that's the distance that the expanding metal has travelled under the impact of the die. But I confess that I haven't studied the phenomenon with the same attention to detail that you are applying.

[jcuve]

Most splits are close to the design, so I would think the sharply demarcated edge of the incuse design elements in the die face initiate the split. When Lincoln's split-line profile is widely displaced from the die-struck profile, I imagine that's the distance that the expanding metal has travelled under the impact of the die. But I confess that I haven't studied the phenomenon with the same attention to detail that you are applying.

Again, thanks for your input Mike. I wish my scope was a little more powerful and I could take a closer look and maybe some sort of evidence would emerge to clarify my question.

...Also, thanks for taking the time to correct my erroneous description of plated Lincolns when I (like many others) referred to them as clad Lincolns in that email the other day.