Old bricks

The blue bricks are fired from clay, which is a product of prolonged weathering of certain aluminum silicate minerals, known for its strong粘性. After mixing clay with water to form brick molds, they are then fired in a kiln (at 900℃-1100℃, for a continuous period of 8-15 days) to create the bricks.

Clay contains iron, which, when fully oxidized during the firing process, forms ferric oxide and appears red, commonly known as red bricks. However, if water is added to cool the clay during firing, the iron does not fully oxidize (resulting in Fe3O4), and the bricks turn blue, known as blue bricks.