What is "clinker brick"

n. a hard brick used as a paving stone [syn: clinker]

Clinker bricks are partially vitrified bricks used in the construction of buildings.

Clinkers are burnt under temperatures so high that the pores of the fuel property are closed by the beginning sinter process and are often mis-shapen. Thus they are considerably denser and therefore heavier and more irregular than regular bricks. Clinkers hardly take up water and are very durable, but have higher thermal conductivity than the more porous conventional red bricks, thus lending less insulation to climate-controlled structures. The name comes from the sound they make when banged together.

In early brick firing kilns called brick clamps, the surface of the bricks that were too close to the fire changed into the volcanic textures and darker/purplish colors. They were often discarded, but around 1900, these bricks were discovered by architects to be usable, distinctive and charming in architectural detailing, adding the earthy quality favored by Arts and Crafts style designers. Modern brick-making techniques can recreate the appearance of these bricks and produce a more consistent product.

In the United States, clinker bricks were made famous by the Pasadena, California architecture firm Greene and Greene who used them (often in combination with native rocks) in walls, foundations, and chimneys.