Generally isn't "stuff", it's damage to the glass. So no you can't soak it off, you have to put a bottle through a tumbler to get the glass clear again. Or I think people use some sort of oil sometimes to hide it, I'm not sure which. Unless you have actual minterals encrusted on the bottle in which case it shouldn't be too hard to scrape off.
New here, but to add to cleaning hints. Two things....white vinehar soak. About an hour?? Then, second, small brushes for dryer cleaning. They have wire bases and longer necks, and short stiff bristles.
One time I saw a photo of an old ink bottle (I collect them) that looked like that. It was held upright in a wire holder that went around near the bottom. There is a place near the bottom of this one...