Distinguishing the Makers of Carnegie Firebricks

By Dan L. Mosier

Carnegie firebricks were made by three different brickmakers in California. Knowing the maker of a Carnegie firebrick is important for assigning the correct date to the brick and, therefore, the site where these bricks are found. This article will show how to distinguish the three different Carnegie firebricks so that they may be attributed to the correct brickmaker. The distinctions shown here only apply to firebricks. It does not apply to other types of brick made by the original Carnegie Brick & Pottery Company. We will begin with a brief history of each of the brickmakers who made Carnegie firebricks.

The Carnegie brand of bricks was first introduced by the Carnegie Brick & Pottery Company at Carnegie, San Joaquin County, California, in 1903. This company made all types of bricks, which included red pressed, buff pressed, enamel face, paving, and firebrick. Its alumina firebrick, using white kaolin clay from the Eocene Tesla Formation, was very popular and dominated the western firebrick market. The Carnegie brickyard produced tens of millions of firebrick. The firebrick was made using both the soft-mud and stiff-mud processes. The soft-mud process molded bricks in a brick press. The stiff-mud process used an extruding machine and wire-cutters to make the bricks. In both cases, every brick was stamped with the CARNEGIE brand name. These firebricks were made in round downdraft kilns with firing temperatures up to 2000˚ F. The last brick was made in 1911, when the brickyard closed.

In 1912, following the closure of the original Carnegie brickyard, the manager and some of the employees went to Stockton to work at the Stockton Fire & Enamel Brick Company. They brought with them the recipe for Carnegie firebrick and so production continued at that brickyard. The Carnegie firebricks were made using the stiff-mud process, or wire-cut firebricks, and brick press machines that made pressed firebricks. In 1920, this company changed its name to the Stockton Fire Brick Company in order to concentrate on just firebricks. The Stockton Company mined clay from its pits at Ione, Amador County, supplemented with clay from Lincoln, Placer County. The clay deposit was part of the Eocene Ione Formation. Quartz grog added to the clay was mined at Amador and Placer counties. The clay was calcined to make alumina flint-clay. The bricks were fired in round downdraft and tunnel kilns up to 2,680˚ F, which was its high-duty firebrick. The company became the largest firebrick producer on the west coast. In 1930, it expanded with a new refractory manufacturing plant at Pittsburg in Contra Costa County, California. Here the company made both wire-cut and pressed Carnegie firebricks, along with other brands.

In 1943, the Stockton Fire Brick Company was purchased by Gladding, McBean & Company, whose main yard was at Lincoln, Placer County, California. Gladding McBean continued making Carnegie firebricks at the Pittsburg yard, using the stiff-mud wire-cut and high-powered dry pressed processes. The clay came from its pits in the Eocene Ione Formation at Lincoln, Placer County. This company used some of the same equipment and kilns as the former company. In 1962, Gladding McBean was merged with Lock Joint Pipe Company of New Jersey and they became known as INTERPACE. As far as could be determined, INTERPACE continued the manufacture of these firebricks until 1982, when they sold the Pittsburg brickyard to North American Refractories Company, which closed the yard.

Carnegie brick samples used for this study were collected from the Carnegie brickyard site at Carnegie and the Gladding McBean brickyard site at Pittsburg. Unfortunately, no Carnegie firebricks could be found at the Stockton Fire Brick Company’s brickyard site, so  samples were obtained from other sites. Other Carnegie firebricks that were found elsewhere or donated by others to the brick archive were identified and supplemented the information used in this study.

There are two ways to distinguish Carnegie firebricks from the three mentioned brickmakers. The first and easiest method is by its clay body components. The second is by the subtle differences in the Carnegie markings. Because these firebricks were often used in extreme heat conditions, the external features of the brick are easily destroyed, making it difficult to see the diagnostic marks. But under extreme heat, melting of the interior of the brick can also make it difficult to see the components. So this identification method will apply to bricks that have not been altered too badly by heat.

Clay Body Components

The interior clay body of Carnegie firebricks can reveal differences among the brickmakers. These firebricks are composed mostly of alumina clay, quartz, and iron oxides in varying proportions and sizes. The clay texture in all of the firebricks is granular clay ranging from fine to coarse grained (<¹/₁₆ to ¹/₄ inch across). The clay body is absent of pores. The visible clasts range from ¹/₁₆ to ¹/₄ inch in size.

Carnegie Brick & Pottery Company

The firebricks made by the Carnegie Brick & Pottery Company are composed of mostly white alumina clay with minor spots of black iron oxides. The clay is subangular to subrounded white kaolinite. This gives the brick a white color.