About 10 years ago, I was really into borosilicate glass and bought a lot of it. (I still can't help but look at it...) I would find it at markets and festivals and buy it right away, ending up with a huge amount... I'm selling some of it little by little. It's made of borosilicate glass, which is melted using a high-temperature oxygen burner. Borosilicate glass is highly transparent and has excellent heat resistance and strength. This is a glass ring. The size is about size 20. Because it's handmade, the size may vary slightly. Ring Size... Size 20