A glass-shader produces a render like this:
Adding a transparent shader creates
Where does the border labeled as 1 come from? Why is the outer region (2) more translucent than transparent? Not sure this is a material or lighting issue.
With out a subsurf modifier it looks terrible:
I tried several values from the IOR range 'Glass': 1.440 - 1.900
Only the upper edges and bottom are beveled.
There are a couple things going on here:
The glass is not entirely white, so a noticeable amount of light is being absorbed. Setting it to white (or almost white) gives a more glassy result:
With a less uniform lighting/environment the glass is more visible:
In this render I adjusted the model to get rid of the subsurf artifacts and thicken the bottom a bit.
There is an air gap between the liquid and the glass. This isn't the way liquid normally sits in a glass in real life, so it might look funny. See Liquid / glass interface IOR and normals in Cycles.
If the interface between the liquid, air, ice, and glass are setup as described, you get a result like this:
the #1 region is caused by the IOR of the Glass that means it is present even in the first render but adding the transparency make it more visible as in the second render you can play with the IOR to see how it effects the shape of that region ; and change the Fac to see were is the transparency applied note : "the region is darker because it is the refraction of the liquid inside the glass"
