Bricks are available in a wide range of colours, which are determined by impurities in the clay.
The best bricks often combined plastic or mallable clays with sandy or more brittle clays, to overcome the tendancy of the softer clays to shrink during firing. The bond is the way in which bricks are arranged in a wall, it is necessary to prevent the vertical joints in two consecutive courses being positioned directly above one another, as this weakens the construction. The importance of brick making to the building industry can be gauged in the fact that between 1820 and 1850 over 100 brick making machines and kilns were patented. This standardisation very often meant the loss of character and colour, as a result, it is always worth making every effort to salvage old bricks for reuse. They can have a wonderful texture, often caused by the sand sprinkled into the mould to stop the clay sticking to it.