Bubbles on the bottom glass bubbles I see bubbles on the bottom of some wine bottles and glass bottles. How is this done?

This kind of glass is usually made by hand.

The bubbles at the bottom are blown out manually with pipes. When the picked glass is still in a molten and soft state, the workers use the metal tube at the bottom to blow out bubbles. After extubation, the soft glass will melt by itself because of the small hole in the nozzle, and the steam drum will stay inside.