Clay bricks are fired from clay, which is a product of prolonged weathering of certain aluminosilicate minerals, known for their strong粘性. After mixing clay with water, the brick molds are formed and then fired in a kiln (at 900℃-1100℃, for 8-15 days) to produce the bricks.

Clay contains iron, which, when fully oxidized during the firing process, forms iron(III) 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 (forming Fe3O4), resulting in a blue color, known as blue bricks.