depression glass

[angelize]

I was playing around with blender's sculpting mode, with a simple model that at the time I thought looked like a clay pot. I gave it a pink colour and then wondered what it would look like rendered as glass. I think it came out looking like a piece of depression glass, however there is a problem.

There is a band at the bottom that does not, render as transparent I've played with all kinds of settings trying to figure this one out ?? Any ideas as to what may be going wrong?

I've attached the packed blend file