This photo is from our building's foyer, built circa 1920. The light coming through the front door windows refracts in the old glass panes, creating beautiful, ripple-like patterns. Our living room windows have the same effect but it was only after a recent window washing that the wavy reflections really started to shine...
Anyone with an old home is probably familiar with this glass — made from different hand blowing or primitive machine methods in the late 19th, early 20th Centuries — with a much lower optical perfection compared to glass manufactured today. Like they say, they don't make it like they used to and, personally, we love the charm it brings to our space.
The big downside to having a house full of antique glass window panes is when it comes time to replace them — the effect won't be the same as you can see with the bottom right pane in the photo above. There are companies out there collecting and reselling old glass but it's not cheap.
It is interesting to us that in trying to perfect glass windows, all character has been lost, making the older stuff more desirable. The common misconception that glass is a liquid and therefore all glass will eventually look rippled if given enough time is simply not true. Glass may be a liquid (arguably) but it is also very stable meaning that distortions and refraction effects are directly related to the manufacturing process. So if you just bought windows, they're always going to look "perfect."
Does your building have old glass? Do you love it or hate it?