"Azure after rain" is the top grade of blue and white porcelain. It is extremely rare and is also the most beautiful color. Blue and white porcelain, also known as white ground blue and white porcelain, its English name is blue and white porcelain. It uses cobalt ore containing cobalt oxide as raw material, depicts patterns on the ceramic body, then covers it with a layer of transparent glaze, and fires it once with a high-temperature reduction flame. Cobalt material turns blue after being fired, and has the characteristics of strong tinting power, bright color, high firing rate and stable color. The earliest blue and white porcelain specimens discovered so far are from the Tang Dynasty; mature blue and white porcelain appeared in the Yuan Dynasty; blue and white porcelain became the mainstream of porcelain in the Ming Dynasty; and it reached its peak during the Kangxi period of the Qing Dynasty. During the Ming and Qing Dynasties, varieties such as multicolored blue and white, peacock green glazed blue and white, bean green glazed blue and white, blue and red glazed blue and white, yellow ground blue and white, Ge glazed blue and white were also created and burned.