Creating Believable Materials - Photographic Rendering with V-Ray for SketchUp - page 219

Currently, the IOR value inside the Refraction controls for this material is set at 1.6 ,
which should work very nicely. If, however, we wanted to give the impression of a
somewhat denser/thicker glass, we could increase the IOR value to give us a some-
what stronger refraction effect. I would, however, strongly recommend that you per-
form quick test renders with your chosen IOR settings, especially rendering the glass
from different angles before committing to it and then rendering at higher quality set-
tings.