2. "Listen" is the sound made when knocking on the jar. If the sound is crisp and pleasant, it means that the porcelain tire is fine and dense without cracks. When fired at high temperature, porcelain is complete. If the sound is dull, it can be concluded that the porcelain tire is cracked or the porcelain is incomplete. This kind of jar is easy to crack and leak after hot and cold changes.
3. "Testing" means testing water, leakage and pressure. Fill it with water and let it stand for more than three days to determine whether the jar body leaks.