which leg is positive in a tantalum capacitor
The radial-leaded caps that are commonly mounted on boards these days mark the negative side.
I have some old axial-leaded caps, and the convention was: if there was a band, the banded side was the "ground" side for nonelectrolytics. Very old electrolytics marked both the + and - sides. Later, marks for one side was dropped - in most cases the minus side was dropped, and the "plus" side was marked with a printed "+", sometimes with a crimp as well. Apparently, some manufacturers kept the band convention, with the "ground" side being the negative side. Nowadays, you'll see axials crimped on the plus side and have arrows pointing to the negative side. I don't recall seeing any tantalums marked any other way than on the + side.