I'm building a weather station, and part of that is getting the UV index via a sensor. Obviously it needs to be exposed to the outside, but you can't use just any material. Most materials such as glass or clear plastics either restricts UV from passing or blocks it completely.
I went hunting for a solution, and there are pieces of quartz glass that you can use, but most of them have a ridiculous price on them since they're selling these to laboratories.
After thinking about it for a while I came up with a cheap and easy solution. Grab yourself an old EPROM, they are erased with UV light so the chip has a UV clear quartz window on it. They are usually a pair of ceramic slabs, one with the window, and one with the bare die of the chip. I got the chip to split in half without cracking or breaking the window. I clipped off all the leads, put a knife on the part where the two halves are joined together and got a clean break on the second try. You can get these chips cheaply, even more so since you don't need a working chip, just the window.