Well, "Pompeii beads" helps to explain why they were called "Lava beads" by the person I bought them from!
You can create a bubbly rough texture when you melt enamels by mixing in impurities such as sawdust or something else combustible at a high temperature in the glassy mixture. When heated in the kiln the glassy ingredients melt and fuse but the added bits burn and create both black smuts and popping bubbles.
Probably quite a firework display within the kiln!
Stefany