When was the blue brick in Shuihongkou?

Mid-Qing Dynasty (1736 to 1850). Shuihongkou blue brick, also known as Hongkou blue brick, is a unique building material in China traditional architectural culture. Shuihongkou area is the origin, hence the name. With its unique color and texture, good air permeability and decorative effect, it is widely used in ancient buildings, palaces, gardens and modern villas.