Gongdao Bei(Fairness Cup, Serving Pitcher) also called the Chazhong or Chahai, is used for holding and mixing the tea liquor.
When brewing tea, the tea liquor is poured into a serving pitcher to prevent tea leaves from over brewing and getting stronger or bitter. The fairness cup(serving pitcher) normally is larger than the matching pot or covered tea bowl.
The common Gongdao cup is of porcelain, purple-clay and glass, with or without handle.
Glass serving pitchers are more popular due to the transparent character. You could enjoy different color of each infusion.