I'm asking about the glass found in old windows. It is not just dirty, scratched, or with varied roughness, but it has irregular imperfections in the glass that make all sorts of distortions. Both when looking through the glass (like in the image below), but also and to a greater extent when looking at the reflections.
Image by TTaylor on wikimedia commons
Image by Stanzilla on wikimedia commons
So how do I make this type of glass in a cycles material?