[Fernando Tella]

That's refraction, isn't it?

Low down IOR index to 1,33 or so.

[Fernando Tella]

Some tips:

-Maybe your glass is too thick cause the refraction effect is too strong; half cm. should be fine.

-IOR has nothing to do with transparency, just with refraction. Make it less transparent with transmitance color; a very light green or blue would make it.