Today I'm discussing using bump maps for reflections in glass. I usually see glass reflections in 3D having perfect reflections. You never really see this in reality though. There is always some bend and distortion in the glass. There are others that do use a bump map to have the reflection act more realistic. Often though, a noise map is used in the bump slot, and I haven't seen this done properly.
In reality each pane of glass has air pressure on it, forcing it to bow in or out. The frames or mullions keep the edges in place though. There is nothing wrong with using a noise map for the bump, it's how it's distributed throughout the glass between the glass frames. Often I see the same noise map passing from one pane of glass to another. That is incorrect.
The trick to getting the same map on every face is using the UVW modifier on your glass and selecting Face for the Mapping type.