I have a GE 4w Ozone Lamp. It is the typical intermediate base style that has a "V" shaped filament with emissive ends, designed to be run on a simple current limited 120V or 240V supply. Here is a picture:

https://www.lighting-gallery.net/gallery/displayimage.php?album=lastup&cat=0&pos=1&pid=255921

As you probably can't see, the feed through leads are not molybdenum foil, and the pinch seal seems to be made while the glass was in a very flowy state, with all rounded edges. This almost completely eliminates quartz as a bulb material, right?

If this is indeed not quartz, then what is it made of? It definitely makes plenty of ozone, it stinks!

Any ideas?

UV-transparent glass not necessary have to be a quartz. Very pure silicate glass (called Uviol) does this too. In a regular soft glass major offenders are metal impurities, ever-present iron atoms usually. Main advantage of Uviol glass is easy processing compatible with regular soft glass by coefficient of expansion, hence you see red dumet lead-ins. Disadvantages are still some UV loss and compared to quartz it loses transparency over time relatively quickly. I bet because of UV-induced decomposition and also by surface reaction with mercury. Still, such glass is commonly used in germicidal tubes.

Also, for example, usual borosilcate glass passes a bit of UVB.

A-ha! I had no idea that it was the impurities that blocked the UV. Nice to know!