When watching the glass blowers, it was interesting to learn that many of them started as potters before learning that art. I've often heard the analogy of God as the potter and us as clay. The idea of refining glass being similar was again brought to my attention in the suggested verses for Advent.
"Behold, I send my messenger to prepare the way before me, and the Lord whom you seek will suddenly come to his temple; the messenger of the covenant in whom you delight, behold, he is coming, says the LORD of hosts. But who can endure the day of his coming, and who can stand when he appears? "For he is like a refiner's fire and like fullers' soap; he will sit as a refiner and purifier of silver, and he will purify the sons of Levi and refine them like gold and silver, till they present right offerings to the LORD. Then the offering of Judah and Jerusalem will be pleasing to the LORD as in the days of old and as in former years."