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[The following text is excerpted from a manuscript titled, "The Laguna Limekilns: Bonny Doon," pp. 64-69. It is copyrighted 1996 by the author. It is used here with permission.]
The presence or absence of firebricks at an industrial site, and the names found on these bricks, is revealing. Several shapes of firebrick (regular, arch, and wedge), and many different named brick, were found at the Laguna limekilns. Most of these were probably imported. Some of these have also been found at other sites in the Santa Cruz mountains, but three are unique to this site. Of those, one has never been reported before!
The practice of stamping, or "branding," the manufacturer's name on a brick goes back to ancient times and was still in vogue at the time these kilns were operating. There are currently only one or two brickmakers in the United States that stamp their name in their brick. The introduction of high speed brickmaking machines made this impractical. Most of the industry stopped this practice forty to fifty years ago as it was an unnecessary, time consuming step.
Fireclay was found in shallow pits and used to make crucibles as early as the 1700s in Europe. The Industrial Revolution brought about the demand for high quality refractory bricks as new equipment and systems were developed. The demand for coal also increased and high grade coal had to be mined at greater depths. It is ironic that the best fireclay was found in conjunction with these deep coal deposits.
The early Spanish and Mexican kilns probably did not utilize firebricks. Most likely they were first imported sometime after 1850. From the early 1850s to the late 1870s firebricks had to be imported to California. At first, the only sources were Scotland and England. A unique find at the Laguna kilns revealed that Belgium also provided bricks. Firebricks (also called refractory, or kiln bricks) were made of higher density clay which was sometimes pressed to remove air and water, enabling the brick to withstand high temperatures. Common building bricks were used on occasion, but these could not hold up as well to high temperatures. Vitrified common and firebricks have been found melted, blackened, and glazed at several kiln sites. Firebricks were made in Europe and shipped (as ballast) "around the horn." At ten cents a brick delivered, the brickyards of the mid-west could not compete. The cost of hauling brick overland was prohibitive. Eventually good quality clay was located in California, but it was not until after the 1910s that production exceeded imports. With the threat to shipping during world war I all imports ceased and were never needed again after the war as the country had become self sufficient.
As the industries on the West Coast developed, steam became an important energy source. This, in turn, was generated in boilers by burning wood fuel. In the Santa Cruz mountains redwood was the preferred fuel as it burned hot, slow and steady. "pine" (actually fir), oak, and madrone were also used. Railroad locomotives, "donkey" engines, steam schooners, loading chutes, and even the fog horn at Pigeon Point Lighthouse were steam-powered. With steam power the brick lining the fireboxes of the boilers required frequent replacement. Although such equipment was used in the Santa Cruz mountains, most of the firebricks are found at limekiln sites. In the early 1900s firebricks were also used to line local sawmill incinerators and fireboxes of boilers at the canneries and food processing plants.
Besides being used for lime production, kilns were also used for brickmaking, lumber drying, and hop and apple drying. The arches of field kilns used for making brick were often lined with firebrick as this location got exceedingly hot. The other types of kilns did not get hot enough to warrent the use of firebrick. But limekilns generated high temperatures (up to 2200 degrees Fahrenheit) to convert the limestone ore into lime, and since the "kills" themselves were made out of limestone the walls had to be shielded to keep them from "cooking" into lime and crumbling!
Stamping names on bricks was a matter of pride or politics, but it also created a depression which would not only save the brickmaker material and make the brick lighter weight, but provided a "key" for the mortar to penetrate. Thus, when the mortar hardened the upper and lower bricks were interlocked. Most of the brick found at the Laguna limekilns are hand-stamped. This is the reason that the name appears at different locations on the surface of the brick, and that the "b" in Snowball was found rotated in two bricks.
Some names set within a depressed frame, called a "frog," had either depressed or raised letters. The frogs had various shapes: rectangles, rectangles with scalloped corners, diamonds, triangles, circles, eyes, and various other shapes. Some frogs also had beveled or curved edges. A brick with a frog would also require less heat to harden it, therefore resulting in a savings of fuel in its manufacture. Also, less weight meant lower shipping costs.
In 1891 Congress passed the "McKinley Tariff Act" which required that imported products be identified as to their country of origin. This may have caused some brickmakers to stamp their names and countries in their brick, but others may have already been doing it out of pride. Regardless of the reason, an evaluation of the bricks found at a site can be helpful in dating the site and establishing the flow of goods.
Firebricks found in limekilns are usually used as a lining and are therefore not an integral part of the structure. Finding a particular named-brick doesn't necessarily date the site. It only provides a possible date that the brick itself may have arrived on the scene. Knowing when a brickyard started using a name might be helpful, but the age of the structure could be older than the brick if the brick was brought in at a later date to line an existing structure. Conversely, finding an old brick at a site does not preclude the possibility that a brick was imported at an earlier time, before the kiln was built, and reused subsequently at the time the lining was last installed. Knowing when a brickyard stopped using a name (or went out of business entirely), reveals the minimum age of the brick, not the structure.
Or, as more aptly stated in "Brick Bats for Archaeologists: Values of Pressed Brick Brands," by Roger and Marsha Kelly: ".... Reuse of bricks is an important capability which may lead to ambiguous interpretations of chronology ... "
Bricks come in all different shapes, sizes, and colors. Shapes vary from cylindrical, square and triangular, to the rectangular ones we see most frequently. Sizes vary as shrinkage of the clay, while it is burning in a brick kiln, is difficult to control. Also, originally there were no standards for size, but common building brick tended to be smaller than firebrick. Generally the firebrick imported to Santa Cruz was 4 1/2" wide x 9" long x 2 1/2" thick. (the newer ones found here are a little smaller: 4" x 8 1/4" x 2 1/2".) The common vary from: 4" x 8" x 2 1/2" to: 4 1/8" x 8 1/2" x 2 3/8". Firebrick is seldom, if ever, red like common building brick. Iron in the clay turns these brick red when they are burned in the brick kiln. Since fireclay is different, the firebricks come out yellow to beige, and darker brown to light grey colors.
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