The deep bowls like this one are usually used during cold weather as they keep the tea hot for long. Thick walls stay lukewarm and won’t scald your fingers. The vessel is covered with famous crackle glaze. This effect is created with the help of so called craquelure technique when the glaze shrinks more than the porcelain. If you continue to drink tea of the same type from the same "crackled” bowl, the infusion will reveal more and more flavors and hues in the course of time.