You make glass by mixing together some materials like sand, limestone and soda, heat them above 2000o F, then cool the incandescent liquid carefully so that crystals cannot form.
Craftsmen on Earth have followed this basic recipe for millennia. It works.
But it works even better in space.
In microgravity, though, you don't need a container. In Day's initial experiments, the melt--a molten droplet about 1/4 inch in diameter--was held in place inside a hot furnace simply by the pressure of sound waves emitted by an acoustic levitator.
Containerless processing produces a better glass.
To his surprise, though, the glass was of even higher quality than theory had predicted.