Pitting

In my hunts, I come across many pans that are pitted on the bottom in the center. I believe I've read on CIC that this is from the sulfur that used to be in natural gas, hence it's "more vintage" than others. But an elderly collector that I talk to says he used to work in a foundry and the pitting is from wet sand in the mold. Which version is more correct?

Also, I have tended to stay away from pitted pans mainly for the look of them, but party for the collectibility.

Any thoughts?

Also from coal. You'd have to wonder why the pitting is always confined to the bottom center or thereabouts, and also why a maker like Griswold would let so many pans leave their foundry with the company name obliterated. Perhaps wet sand can cause a similar defect, but pieces so-affected would most certainly have been thrown on the scrap pile to be remelted.

I wonder if he was referring to a cast shift. At least that's what I think it's called.