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Tile Production at the Santa Barbara Presidio: Part 1, Mining and Processing Raw Clay

by Mike Imwalle

Fired clay tiles were introduced as a building material at the Santa Barbara Presidio early in its development. Floor tiles, or ladrillos, were fired at the presidio for the construction of the presidio aqueduct by 1784. By 1786 enough roof tiles, or tejas, had been made to cover the buildings of the first wing of the presidio quadrangle. This is the introduction to a three-part series on tile production at the Santa Barbara Presidio.  Part one will summarize the mining and processing of raw clay, part two will outline the tile fabrication process, and part three will examine the firing process.

A portion of the 1852 U.S Coast Survey “Map of the Port of Santa Barbara, California” showing probable location of area utilized for clay extraction during the 18th century presidio construction.

The site of the Santa Barbara Presidio was chosen for strategic purposes, but also for its proximity to valuable resources for construction. The site was covered with sandy loam topsoil ideal for making sun-dried adobe bricks.  A thick layer of well-developed yellowish brown, sandy clay lies just beneath the topsoil used for making the adobes.  The only way to get to the underlying clay layer is to remove the entire layer of topsoil or to dig into the clay layer from the side.

(l) Anacapa School intern Brookes Degen with more than 2000 lbs of raw clay excavated during the Northwest Corner Reconstruction Project. (r) Raw clay soaking in barrels of water. Photo by Mike Imwalle.

The area where presidio soldiers and Chumash laborers mined clay for the presidio tiles was likely due north of the quadrangle on  a north-facing slope above the slough or estero. During the reconstruction of the new Northwest Corner Visitor’s Center in 2007, clay was excavated from the bottom of the foundation trenches using a backhoe. Mineralogically it is identical to the clay mined for Presidio roof and floor tiles more than 225 years ago.

(l) Anacapa interns Josh Figueroa, Aubrey Cazabat, and Wishiah Roper pushing wet clay through a screen to remove roots, rocks, and other impurities. (r) Close-up of clay slurry being prepared for drying and bagging. Photo by Mike Imwalle.

For the past six years, we have been using experimental archaeology to replicate historical fabrication and firing techniques for tile and pottery.     Archaeological interns from The Anacapa School assisted with the processing of the clay. First, the raw clay is soaked in barrels of water for several weeks to liquefy the material for screening. Next, the clay is pushed through screens to remove roots, rocks, and other impurities. Once the clay has been screened, it’s time to remove some of the excess moisture. The liquefied clay slurry is poured into cloth bags to assist with the evaporation of water from the clay. Once enough water has been evaporated for the clay to be stiff enough to mold, it is bagged in plastic for storage and transported to the pottery shop for fabrication into tiles and other vessels.

Brookes Degen finishing the clay processing. (A) Pouring clay slurry into cloth bags for partial during. (B) Removing partially dried clay from cloth bag. (C) Transferring processed clay to plastic bags for storage. (D) Finished product: a twenty-five pound bag of processed clay ready to be transported to the pottery shop for fabrication into tiles. photo by Mike Imwalle.

The next installment of this post will examine the actual fabrication process, then, finally, a summary of the various firing techniques likely used for producing tile at the Presidio.

Mike Imwalle is the archaeologist at the Santa Barbara Trust for Historic Preservation.

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