Plating Split-Doubling (AKA Split-Line Doubling):
At this point there is no official phrase for this phenomenon; web searches lead Plating Split-Doubling to Ken Potter and Split-Line Doubling to Mike Diamond, but it is unclear who coined either term. The characteristics are: a split in the copper, revealing a light blue to greenish area (which is exposed zinc), that shadows a device and makes it appear doubled.
Plating Split-Doubling is notoriously misidentified as RPMs, Doubled Dies and on Broadstrikes as having been Double Struck (when it has not).
The phenomenon is commonly located on either the obverse or reverse of copper plated Lincoln cents. Plating Split-Doubling is also boldly found on some Broadstrikes and Off-centered Lincoln cents. While it can be found almost anywhere, it specifically tends to inhabit the regions nearest the rim and is associated with the design elements. The devices most frequently identified on a normal strike are the mintmark (MM), USoA, INGWT and sometimes parts of the memorial. The split itself can be very thin and hug a device or some distance from a device and wide to the point that it appears almost comical on some Broadstruck Lincolns.
While it would seem possible that the split is a tear that is facilitated by the raised struck parts of the coin holding the copper in place as it travels too quickly and too far – it appears more likely the sharp edge of the incuse die devices weaken and help to instigate the copper to split open and reveal the zinc as the copper it is stretched too thin. Why it happens inconsistently appears unknown.
Below are two examples: the obverse of a 1993 Off-center Lincoln and the reverse of a dateless Broadstruck Lincoln, both exhibit Plating Split-Doubling. The Off-center has the appearance of an extra profile while the Broadstruck has various parts of the memorial splitting open. Points 1, 2 & 3 (on the illustration below) appear to originate from the same location at the first moment of impact next to the portrait of Lincoln, and then they appear to travel apart as the copper is over stretched.
Below is a 1992D and a 1989D both with commonly seen Plating Split-Doubling on the MM and the devices on the reverse, notably USoA and the memorial. The black arrows in the first photo show the splits while the white arrows show mild Machine Doubling that has also occurred.
Here is the approximate distance for specific devices from the rim on Lincoln cents:<
Bottom of bust: .6mm (not sharp)
ONE CENT: .2-.4mm
Most splits are occur on LIB, the upper parts of IGWT, USoA, the lower parts of ONE CENT, the date, the outer parts of the memorial and, while not as close to the edge yet yielding many examples, the lower and inner loops of the D MM.