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.
Stockton Fire Brick CompanyThe firebricks made by the Stockton Fire Brick Company contain mostly subangular cream flint-clay with about 3% subangular white quartz and 3% round black iron oxides. The cream flint-clay gives the brick a yellowish color. Visible white quartz grog, mostly 1/16 to 1/4 inch across, is a diagnostic mineral for this firebrick when present.
Gladding, McBean & Company
The firebricks made by Gladding, McBean & Company are composed of subangular cream and gray flint-clay with minor rounded black iron oxides and rounded white flint-clay. The flint-clay has conchoidal fractures. The proportions of the cream and gray flint-clay dictate the brick color ranging from yellowish to buff, respectively.
The differences in the clay body components of these firebricks can be seen in the following table.
Table 1. Clay Body Components.
Rocks (volume %)
Carnegie Brick & Pottery Co.
white alumina clay (95), iron oxides (5)
Stockton Fire Brick Co.
cream flint-clay (94), white quartz (3), iron oxides (3)
Gladding, McBean & Co.
cream and gray flint-clay (98), iron oxides (1), white flint-clay (1)
Table 2. Exterior Features and Manufacturing Years.
Carnegie Brick & Pottery Co.
Stockton Fire Brick Co.
Gladding, McBean & Co.
Carnegie MarkingsCarnegie brand markings and name plate or frog can also be used to distinguish among the firebricks made by the three brickmakers. Use these features along with the clay body components to determine the brickmaker. A frog is a deep depression usually on the face of the brick and usually deeper than 1/16 inch that frames the brand name. If it is shallower, it is called a name plate imprint. The following measurements are for standard size firebricks, not blocks or special shapes. Only the firebricks from the Carnegie Brick & Pottery Company has a rectangular frog, about 1/8 inch deep. Its name plate imprint can be rectangular or extend across the whole length of the brick. The firebricks from the Stockton Fire Brick Company will show either a rectangular name plate imprint or no name plate imprint. The firebricks from the Gladding, McBean & Company will always have a rounded rectangular name plate imprint, which is diagnostic for these firebricks. The length of the frog or name plate and name span can vary greatly among these firebricks. The lengths may be related to the size of the brick, but not always. Generally, the firebricks from the Carnegie Brick and Pottery Company have a larger frog up to 7 x 1 1/4 inches or a name plate imprint that spans across the length of a brick. The name span is up to 6 1/2 x 1 inches. The name plate imprint in the Gladding, McBean & Company ranges from 6 1/4 to 6 1/2 x 1 inches. The name span ranges from 4 3/4 to 5 3/4 x 3/4 inches. One example for the name plate in the Stockton Fire Brick Company is 5 5/8 x 3/4 inches and the name span is 5 to 5 5/8 inches.
Individual letters also show some differences among Carnegie firebricks by the different brickmakers.
The largest distinctions can be made with the typology between the Carnegie Brick & Pottery Company and the Gladding, McBean & Company. The distinction is less so between Gladding McBean and Stockton Fire Brick Company. The letters in all three companies are recessed on a face of the brick. Usually, the letters in the Carnegie Brick & Pottery Company and Stockton Fire Brick Company firebricks are deep and beveled, but not always. The letters in Gladding McBean are flat and shallow. The letters in the Carnegie Brick & Pottery Company name is 5/8 inch wide. The letters in both Gladding McBean and Stockton Fire Brick Company can be 1/2 inch wide, but some are 9/16 inch wide in Gladding McBean firebricks. The letters for all three companies usually stand 3/4 inch in height, with the exception of 1 inch tall letters seen in some Carnegie Brick & Pottery Company firebricks. The differences for each letter will now be described.
C: The firebricks in all three companies have a curved back C with a 1/8 inch gap. Gladding McBean has some with a flat back C with a 1/4 inch gap.
A: Carnegie Brick & Pottery Company has a cross bar that measures 1/2 inch from the top of the letter to the middle of the cross bar. The cross bars in Stockton Fire Brick Company and Gladding McBean measure 1/2 or 9/16 inch from the top of the letter to the middle of the cross bar. Another diagnostic feature in some of the Gladding McBean firebricks is an A with a rounded top, rather than a pointed top, and vertical parallel legs. Its cross bar is 7/16 inch from the top of the letter.
R: The right leg in the R is angled more in the Gladding McBean and Stockton Fire Brick Company firebricks compared to that in the Carnegie Brick & Pottery Company firebricks, which can have more of a block shape. The shape of the right leg is straight in the Gladding McBean and the Carnegie Brick & Pottery Company. The shape of the right leg is straight or curved in the Stockton Fire Brick Company. Carnegie Brick & Pottery Company cross bar is 3/8 inch long. Gladding McBean and Stockton Fire Brick Company cross bars are 1/4 inch long.
N: A lower case n has been used only in the Gladding McBean firebricks. The other two companies always used the capital N.
E: The middle cross bar in the Gladding McBean is 1/4 inch long for 1/2 inch wide E and 1/2 inch long for 9/16 inch wide E. In the Stockton Fire Brick Company, the middle bar is 1/4 or 3/8 inch long. In the Carnegie Brick & Pottery Company, the middle bar is 7/16 inch long. The top and bottom cross bars correspond to the width of the letters for each of the companies, which are 5/8 inch for Carnegie Brick & Pottery Company, 1/2 inch for Stockton Fire Brick Company, and 1/2 or 9/16 inch for Gladding McBean.
G: The terminating cross bar in the Gladding McBean and Stockton Fire Brick Company is 1/4 inch long. The terminating cross bar in the Carnegie Brick & Pottery Company is 1/8 inch long. Firebricks from all three companies have a curved back G, with the exception of some Gladding McBean that have a flat back G. The letter C has been used to replace G in some of the Carnegie Brick & Pottery Company firebricks.
Thus, the differences in typology can be used to distinguish the standard size Carnegie firebricks from the three companies if the letters are legible enough to take measurements. For special shaped Carnegie firebricks, which have a wider range of sizes, it is recommended that brickmakers be identified by the clay body components. However, if the special shaped firebrick has a rounded rectangular name plate imprint, it should be assigned to the Gladding McBean & Company.
Thanks goes out to James Eric Freedner, Stuart Guedon, Petter L. Rosenquist, George L. Kennedy, Stan Old, Marcy Kane, and Annette Alvarez for contributing some of the Carnegie firebricks used in this study.
Dietrich, Waldemar P. The Clay Resources and the Ceramic Industry of California. California State Mining Bureau Bulletin no. 99, 1928.
Mosier, Dan L. Carnegie Brick & Pottery Company. California Bricks, calbricks.netfirms.com, 2006.
Mosier, Dan L. Gladding, McBean & Company. California Bricks, calbricks.netfirms.com, 2021.
Mosier, Dan L. Stockton Fire & Enamel Brick Company. California Bricks, calbricks.netfirms.com, 2009.
Mosier, Dan L. Stockton Fire Brick Company. California Bricks, calbricks.netfirms.com, 2021.
Citation: Mosier Dan L. Distinguishing the Makers of Carnegie Firebricks. California Bricks, https://californiabricks.com, 2022.