Well yes, there's that but also the molten glass...flux...the more sodium oxide, the slower it solidifies. And if it hardens too fast, I don't have the time to properly shape it.

But I also work with pure sodium to turn glass opaque if that's the look I want, and I use chemicals and well toxins really, like arsenic to remove bubbles from the flux.

You have to know what you can and can't mix together as well as how much to use for a given project. Spills can be dangerous and certainly people who don't know their chemistry can end up seriously harming themselves and others.