The Double Rim appearance to the right of the date is was is called a Misaligned Die Strike. I bet the Reverse side is perfectly centered.
C'mon big money.... I've only come across this one. I'm thinking it was struck at least twice. With the second strike upsetting the copper plating and creating the grainy texture. Mine has a rather square rim and a higher relief than I expect on Zinc cents. Does that sound like the one you have?
The reverse is slightly off center. Is this within expectations? The edge is uniform all around - the 1991d is on the right, on the left is a 2007 (aka the only zinc cent readily available). Any ideas on the grainy texture?
I would definitely say the ram die was not centered properly with the collar. This would allow the coin material to extrude, wire, or fin (basically squirt) out between the gap of the neck of the ram die and the collar where the gap was greatest from the ram die being off center. Since the coin is a 1991 it was either made on a Schuler MRH 150 which has centering screws for the ram die, or it was made on one of the 4 up Bliss 6K 225 presses, which had no real easily adjustable ram die centering system. The Bliss held 4 sets of dies. There were 2 die blocks on the ram of the press, each held 2 dies each. These presses were somewhat complex in thier set up which made them difficult to align aa w dies had to be aligneg at a time. So in my opinion the cent was probably struck on one of these Bliss presses as the Schulers are easy to adjust. If my memory serves me correctly the Bliss presses were in service until the late 90s. Sean
Misaligned dies create the larger looking rim on one side over the other. Often caused by or accompaning misaligned dies are the doubled rims. Doubled rims are often reffered to as finned rims. -SC
Maybe either the right was struck on a thick planchet or the left was struck on a thin. This can occur when either the metal sheet is in the roller machine for too long or not long enough. Try weighing them. They both should weigh around 2.48 grams with a 0.13 gram tolerance. -SC