So most coins that I see that have stripes are referred to as woodies. If a woody is thought to be caused by improperly mixing the different metal alloys that make up the composition of a coin, then what is going on with the 100% zinc coins? What causes the striping like you see on this coin? Is it still considered a woody even though it only has 1 alloy in it's composition?
I also have some, and have seen many zinc coins. I do notice a similarity between zinc coins and copper plated zinc cents that show lines on them, that most people call "Linear Plating Blisters". The creation of the Lines on a zinc coin must be produced by the rollers that flatten the metal strips to the correct thickness for planchets. A groove in the roller will leave a ridge in the metal. And these ridges can oxidize at a different rate than the rest of the planchet if there is ample time between the planchet being made, and the coin being struck. Once this process has started there is no reversal of it. It is hard to believe that these line would still show after the planchet is struck. But they seem to show even after being plated and then struck. An older zinc AU coins show this feature the best, as does an AU copper coin show it's Woody effect.
This seems like a very reasonable explanation, thanks. The lines are very nearly parallel so are unlikely to be formed post-striking. Differential rates of oxidation nucleating on scratch sites could account for the color difference even if the oxide thickness difference is slight. As for how the scratches can survive striking, even if the pressure of the strike is high enough to cause plastic deformation of the planchet, it is a fast and low-temperature process which perhaps is not enough to cause much smoothing of the surface at the micro level. It would be an interesting experiment to look at a planchet before and after striking with something like an atomic force microscope to see how much of the surface texture survived. I would bet a lot. Even if the high points are flattened a bit, any grooves or scratches are probably too recessed to be much affected.
