Most bricks turn red when burnt. That is owing to the fact that the clay from which they were made contained a very little iron, and the burning changed this iron into iron-rust, which is of a red colour.

大多数砖在烧过以后，都会变成红色。这种变化的原因是，砖的原料——粘土含有很少的铁，烧砖的过程，把这些铁变成了铁锈，铁锈是红色的。