by Michael Imwalle
The previous installments of this series briefly described the process of extracting or mining clay and the fabrication of roof and floor tiles. This post will describe methods employed for firing roof and floor tiles. Once the molded tiles have been air-dried they are ready to be fired. The drying process is a critical step in tile production. If tiles are not completely dried before firing, moisture trapped in the clay expands as it is heated during firing and the tiles explode. Because the various steps in tile production are so labor intensive it is important to maximize the amount of tiles that are successfully fired. Drying and firing are slow processes that require patience. Trying to speed up either of these to activities will result in the loss of large amounts of tile during firing.
The first step in the firing process is the loading or stacking of the kiln. The unfired or “green” tiles are carefully stacked inside of kilns for firing. The unfired tiles are extremely brittle and great care needs to be taken to stack the tile without breaking them. Roof tiles, or tejas, are typically stacked in rows on end. Floor tiles, or ladrillos, are carefully stacked on their sides with space between them for the hot air and gasses of the kiln to circulate. Leaving air space around the tiles is critical to achieving and maintaining a constant temperature during firing. Without good circulation of air around the tiles hot spots and cold spots can develop within the kiln creating a firing environment that leads to correspondingly over-fired and under-fired tiles.
Although we do not know exactly what type of kilns were used to fire the tiles at the Santa Barbara Presidio, we do have contemporary examples from the period. A sketch of the Monterey Presidio tile kilns depicts circular tile kilns built into the hillside adjacent to the fort. A similar tile kiln has been restored a Mission San Luis Rey de Francia. This type of kiln would have had two chambers. The lower, or firing, chamber was accessed by an arched opening at the bottom of the kiln. This is where the stoker, or quemador, would diligently tend the fire to maintain a constant temperature of around 1800⁰ for up to twenty-four hours.
The upper chamber of an updraft kiln is for the wares, or in this case tiles. They would have been loaded from the top and stacked to fill the upper chamber. The upper chamber is supported by a grate formed by a series of tile arches. Once the upper chamber was loaded with tile the top was covered with adobes or tiles to prevent the hot gasses in the kiln from escaping through the top. Because of the intensity of the fires and duration of the firing process, tremendous amounts of wood or other fuel was necessary to keep the kilns stoked.
Another example of circular tile kilns in Santa Barbara County is the tile kiln documented by Frs. Lynch and O’Brien at the Santa Barbara Mission. Archaeologically, Harrison identified the base of a circular tile kiln at La Purísima Mission in 1940.
A similar kiln was used to fire tiles for the Rancho San Marcos Adobe in circa 1804. While an open-topped square kiln has been identified at San Antonio Mission, documentary and archaeological evidence suggest that the circular kilns were predominant.
Where were the Santa Barbara Presidio kilns? Part one of this series suggested that the clay source for presidio tile was likely located on a slope northeast of the Presidio. Part two of this series documented the fact that the kilns would likely have been located near the clay source. This would place the kilns somewhere near the clay source northeast of the Presidio quadrangle.
While no archaeological evidence of the kilns themselves have been identified in this portion of the site, artifacts recovered during construction monitoring of a nearby development did identify wasted tiles. Three tiles were actually melted together from over-firing. Although this does not definitively identify the location of the Presidio tile kilns, the wasted tiles are evidence of tile firing somewhere in the neighborhood. Stay tuned as we continue our research!
Michael Imwalle is the archaeologist at the Santa Barbara Trust for Historic Preservation.