Excerpts from Bricks and Brickmaking: A Handbook for Historical Archaeology, Karl Gurcke, University of Idaho Press 1987.
"In Philadelphia, for example, the clay was 'dug in spits, each spit being one foot deep, four feet wide, and 16 feet deep, which makes a mass for one thousand bricks.'" Source: "Mease 1813," quoted by Joseph Arnold Foster, ed., in "Accounts of Brickmaking in America Written Before 1850," Contributions to a Study of Brickmaking in America, part 5, Claremont, California: private printed by the author.
"An expert [hand] molder could make between 3,000 and 5,000 bricks in a day if he was kept well supplied with clay."
"Depending on the machine and the number of bricks per mold, an average soft-mud machine had a capacity of between 1,000 and 15,000 bricks per hour."
"Both soft-mud and stiff-mud bricks have one major shortcoming compared to the next category of bricks to be described: they lack uniform sharp edges." "In order to make soft-mud and stiff-mud bricks competitive . . . a machine known as the repress was invented." "When the bricks were dry enough, the repress machine was wheeled out to the yard, the green bricks were placed in the machine, and pressure was applied." "The repress machine produced a smoother brick with much sharper edges. . . . In the case of stiff-mud bricks the repress machine could be used to add the company's name, a step that could not be done mechanically any other way."
"The more primitive updraft kilns may require seven days [to fire a load of bricks], while modern tunnel kilns need only 40 hours."
"Scove or field kilns are made out of the dried green bricks themselves and are temporary in nature. These kilns are constructed in sections of about 35,000 bricks each and piled 35 to 40 courses high. At the bottom of each section an arch or firebox is built that runs the length of the kiln. The arch is approximately two bricks' length in width and is formed by the gradual projection [i.e., corbelling] of the course to a point at which the bricks meet, usually 32 inches from the ground." "After the kiln is set, a wall of burnt brick is put around the kiln and daubed over with mud to prevent unwanted rafts. The arches are left open because through them the fires must be lit and fed until the later stages of burning [the cooling phase], when they are covered with stones or iron doors."
"The hot air and gases simply flow from fires on the bottom up through the kiln and out through the top, with little attempt being made to recirculate the heat. The defects of this type of kiln lie primarily in the unevenness of the burn. The bricks at the bottom receive more heat than those at the top, and as a consequence they vitrify sooner and are crushed by the weight of those above. For the top bricks the reverse is true: they receive less heat and fail to vitrify, and they are exposed to the weather and are generally unusable. Often more than a fourth of the bricks are lost during the course of a burn in kilns of this type."
"'Arch' bricks are those bricks that make up and surround the fire holes, or arches, in temporary kilns or clamps. Because of the weight on top of them and their nearness to the fire, they always are overburned and frequently deformed."
"At the Hidden brickyard in Vancouver, Washington [which operates scove kilns], face bricks are not treated differently from regular bricks; when the burn is complete, the bricks that have received the most even and uniform heat are separated out and sold as face bricks."
"A stick-trimmed surface was presumably made by a wooden strike. As the strike was dragged across the top surface of the brick it carried along with it the harder lumps of clay, bits of organic matter, and small grains of sand or rock. These objects left small grooves or lines in the surface. Blade-trimmed bricks were probably made with a metal plane similar to the one in use at the Hidden brickyard. As the blade was pushed across the struck surface it tended to cut through the clay, leaving small gouges rather than small parallel lines. A soft-mud brick machine needs a metal stick since it may work a clay that is stiffer than clay that can be worked by hand. . . . Figure 27 illustrates the marks left on the struck face by a wooden stick and a metal blade."
"The other main characteristic of soft-mud brick depends on what lubricant is used to allow the green brick to slip free of the mold. Sand gives the brick a rough granular texture on all sides except the struck one. "
"Water, in contrast, often leaves small ripples or 'water marks' on the bottom and sides of a brick. They are similar to the marks left on the bottom of a puddle after the water has evaporated. . . . Water-struck bricks also often exhibit slight vertical [marks] on the sides and ends of the brick. They are caused by 'gritty particles scouring the sides of the [green] brick when it [is] tipped out of the mold.' Sand-struck bricks may also exhibit these lines."
"The difference between hand- and machine-made soft-mud brick is one of degree. Like any product made by hand, the handmade brick exhibits greater variation in both size and shape. It usually varies more in terms of color as well, but that variation is often caused by primitive updraft kilns rather than by the molding process. Soft-mud bricks made by machine are much more uniform in all these respects."
Last revised July 4, 2010