How to make an "old glass" material in cycles? 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

Take a look at the pictures on this site or this page to get more of an idea what I'm talking about in the glass.

So how do I make this type of glass in a cycles material?
for this kind of things you will want to use either a normal map (using the normal map node under Add node>vector>normal map) or a bump map (using the bump node found under Add node>vector>bump) and feed the normal output into the normal input of your refraction or glass shader

Here is an example setup:



And the results this gives:



If you make a proper texture to acomodate for the distortion you are looking for then you should be able to get identical results to the images you provided.

If you decide to use normal maps then you will need to use this fix: www.youtube.com/watch?v=jlOtXtQSxd0