Page 27 - Curriculum Visions Dynamic Book

(Right) Many houses in historic districts are made of brick. That is because brick is much more durable than wood, and so the brick buildings have often survived while the wooden ones have not.
Bricks were first made about 6,000 years ago. Over time the size and shape of the brick evolved. The main factor influencing the size and shape was ease of handling, though bricks also had to be big enough to create a good “footprint” and so a strong wall.
Because brickmaking is usually a local industry, and exports of bricks are small, the size and shape have not been standardized as they have for many other products. So, wide variation is found across the world.
Making bricks does not require pure components in the same way as in the whiteware industry. Indeed, staining by iron and other metal compounds is welcomed to add an attractive colour to the bricks. However, the main concern in making a building ceramic is that it be strong, for houses built with bricks are heavy and put enormous downwards stresses on the lower rows (courses) of bricks. Bricks also need to be able to resist weathering by rain, cold, and heat.
The colour of bricks depends on the amount of impurities in the mixture and on the way the kiln
is operated. Colours ranging from pale yellow through tan, brown, red, and black are possible. However, the metal oxides that cause the colour also act as fluxes, helping reduce the temperature at which the clay begins to vitrify.
The purple colours of some bricks are achieved by a process called flashing. It happens at the end of the brickmaking. The bricks are moved into an oven in which there is a gas such as carbon monoxide that reacts with oxygen in the brick and so takes it away from the oxygen in the iron. That changes the iron oxide (from ferric to ferrous oxide), and the brick turns from red to purple.
Bricks are needed in huge quantities for such basic structures as houses. To keep the prices of
(Below) Red bricks can be used to form a durable and decorative surface, as shown in this street.
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