Which 1971-D Jefferson Nickel Do You Prefer (GTG)

You pretty much answered your own question, as have other posters in the thread. The orange peel effect is caused by severe die wear. In other words it's the metal of the planchets flowing across the exact same areas of the die over and over and over again - thousands of times. But it doesn't always result in the orange peel look, in fact it most often appears as simple radial lines, even in cases of advanced severity.

So why orange peel on a few and plain lines on most ? Well, one way that could be explained is what is said below.

Think of the wear lines on the die as being straight and even grooves, and that's what they always are when they first start. But as the wear progresses, if the die were improperly hardened, meaning the metal of the die is softer, and thus weaker, than it's supposed to be, as the wear progresses and the lines get deeper and deeper and wider and wider, sometimes metal from the sides of those straight and even grooves gives way here and there and is also pulled away leaving kind of like shallow pits in the sides of the grooves. It is these shallow pits that create the orange peel effect.

So sometimes the orange peel effect may be indirectly caused by improperly hardened dies, but it can also be caused by the metal alloy used to make the dies being weaker than it is supposed to be. In other words the dies may have been hardened correctly, but because the metal was weaker than it was supposed it to be to begin with, it gives way once wear becomes advanced enough and also results in the orange peel effect. And it could also be things like impurities in the die metal alloy, also making the metal weaker than it's supposed to be.

Bottom line, it's kind of the same thing, the die metal is not as hard or as strong as it's supposed to be. But there can be various reasons as to why the die metal is not as hard or as strong as it's supposed to be.

In any event, straight radial lines is how die wear is most commonly seen, sometimes with irregularities here and there, but every now and then the orange peel effect pops up.

I would add one more thing that really has nothing to do with the subject being discussed here, but it does have to do with radial lines. As everybody knows it's metal flow that creates luster. And luster is created in radial lines. But most books and most articles that one can read will refer to those radial lines as flowing outwards, from the center to the outer edges of the coin much like the spokes on a wheel. That is the conventional wisdom. But that isn't what happens at all. To the contrary, the metal doesn't flow outwards, it flows inwards - from the outer portions of the planchet towards the center, but still like the spokes of a wheel.

And for those who wish to disagree with this, well you can try but all you have to do is think for a minute. Where does most of the metal on a coin end up ? It ends up in the general center of the coin - where the main devices are. So it can't get there by flowing outwards, it absolutely must flow inwards.

And this is also why the upset mill is used when making planchets, it's to make sure there's enough metal left on the outer edges of the planchet to create the rim. If it wasn't for that extra thickness of metal created by the upset mill, the rim could never form during striking because the majority of the metal of the planchet is going to flow inwards - not outwards.