The color of common bricks depends largely upon the composition of the clay used and the temperature to which they are burnt. Pure clay, free from iron, will burn white, but the color of white bricks is generally due to the presence of lime. Iron in the clay produces a tint which varies from light yellow to orange and red, according to the proportion of iron contained in the clay. A clear bright red is produced by a large proportion of oxide of iron, and a still greater proportion of iron gives a dark blue or purple color, and when the bricks are intensely heated the iron melts and runs through the bricks, causing vitrification and giving increased strength. The presence of iron and lime produces a cream or light drab color. Magnesia produces a brown color, and when in the presence of iron makes the brick yellow.
The color of pressed brick is, of course, the same as that of common bricks made from the same clay; but pressed bricks are also colored artificially, either by mixing together clays of different chemical composition, or by mixing mineral paints or mortar colors with the clay in the dry pan. Bricks are also sometimes colored by applying a mineral pigment to the face of the bricks before burning. This latter method, however, is not very satisfactory. At the present time the use of colored bricks is very popular, and face brick are made in all shades of red, pink, buff, cream and yellow. Some of these colors are very effective when used in an artistic manner, but the use of colored bricks has been much abused, and it requires a fine sense of color to use them effectively, especially where two or more shades are used in the same building.