Category Archives: Archaeology

Tile Production at the Santa Barbara Presidio: Part 3, Kilns and Firing

by Michael Imwalle

Sketch of the Monterey Presidio tile kilns by the author based on the 1791 José Cardero sketch of the Presidio of Monterey.

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.

Large open-top circular tile kiln at Mission San Luis Rey de Francia. Note modern restoration work in foreground with top of circular kiln extending through the top. Photo by author.

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.

Detail of underside of the grate formed by tile arches in the tile kiln at La Purísima Mission State Historic Park. This photograph is taken from in the firing chamber towards the upper chamber. Photo by Mike Imwalle.

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.

Detail of Santa Barbara Mission tile kilns recorded by Fathers Lynch and O’Brien during the 1930s illustrating approximate location of grate supported by tile arches. Adapted by Mike Imwalle.

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.

(top) Sketch of tile kiln excavated by M. R. Harrington, La Purísima Mission, 1940. (bottom) Photograph of the base of the tile kiln at La Purísima Mission 2006 by Mike Imwalle.

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.

Circular, open-topped tile kilns excavated by the author at Rancho San Marcos in 2009. Photograph by Mike Imwalle.

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.

Russell A. Ruiz rendering of the Santa Barbara Presidio quadrangle illustrating possible location of the Presidio tile kilns. Adapted by Mike Imwalle.
Wasted tile recovered during archaeological monitoring at the site of the Inn of the Spanish Gardens. Photograph by Mike Imwalle.

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.  

Tile Production at the Santa Barbara Presidio: Part 2, Forming Roof and Floor Tiles

by Michael Imwalle

Illustration of Presidio-era tile maker. Note the clay pressed into templates in the foreground, slatted forms on work table, and drying rack in background. Courtesy of the Presidio Research Center, artist unknown.

The previous installment of this series briefly described the process of extracting, or mining, clay and processing it to prepare for the fabrication of roof and floor tiles. This post will briefly describe methods employed for molding, forming, and drying tiles prior to firing. In contrast to clay for making pottery, which must be kept moist and pliable during pottery production, clay for tiles needs to be relatively stiff and free of excess moisture. Clay used for the fabrication of roof tiles, or tejas, for example, needs to be moist enough to push into trapezoidal-shaped templates, but stiff enough to remove from the templates and place onto semi-cylindrical, tapered molds. Once the desired barrel shape is realized on the mold, the wet tile was removed to dry on the ground or on racks. Like the roof tiles, floor tiles, or ladrillos, were formed by pushing relatively stiff clay into square or rectangular molds then removing the tiles to air-dry before firing.

Cross-section drawing of the Presidio Aqueduct illustrating the use of floor tiles, or ladrillos, as a base. Based on an original drawing by Pamela Easter.

Tiles were probably made relatively close to where the clay was mined and where the tiles were ultimately fired in kilns. Kilns are typically located close to the clay source (see previous post for possible clay source location) and downwind from residences to avoid the risk of fire and excessive smoke and ash. Kilns are also located relatively close to construction sites so as to cut the cost of transportation and reduce the amount of breakage during delivery. We know from archaeological and historical evidence that ladrillos were fired for the presidio aqueduct by 1784. By 1786, thousands of tejas had been installed on the first wing of the adobe quadrangle and thousands more were ready for firing.

Photograph of a trapezoidal template packed with wet clay (left), slatted mold (center), and finished tile (right). Photograph courtesy of the Edith Webb Collection, La Purísima Mission State Historic Park.

During the presidio era, templates, or forms, for roof tiles would have been constructed of hand-planed lumber fashioned to the desired thickness of the tile.  Molds for the tiles could be fashioned in a number of ways, including forms carved from a single piece of wood and forms assembled from semicircular pieces of wood attached with wooden slats. Legend has it that roof tiles were formed on the thighs of “Indian women.”  Although forms could be fashioned from a variety of materials, according to archaeological evidence, thighs do not appear to have been one of them!

Variety of roof tiles and molds (A) Tapered tile mold carved from single piece of wood. (B) Intact original Presidio roof tile excavated from the Northeast Corner site, (C) Slatted form used for La Purísima Mission reconstruction, (D) Example of slatted form with cloth cover, (E), Plaster of Paris form molded from original Presidio roof tile, and (F) Roof tile replicated from original Presidio roof tile.
Anacapa School interns Josh Figueroa, Wishiah Roper, and Aubrey Cazabat packing wet clay into template, (B) removing clay from template, (C) placing clay on plaster of Paris form, and (D) Wishiah, Josh, Aubrey, and Amanda Lyons with the finished teja. Photo by Michael Imwalle.

During an attempt to replicate tile manufacturing and firing processes for the Smithsonian-sponsored “Ceramics Rediscovered” exhibit, SBTHP archaeologists used plaster of Paris to make a mold of an original presidio roof tile to insure accuracy in the replication process. Each 24-inch-long roof tile that tapers in width from 12 inches to 8 inches takes approximately 25-30 pounds of wet clay. Due to the fact that the wet clay shrinks about 10-12 percent when it dries, the molds need to be made slightly larger than the desired finished dimension of the tiles. Once the tiles have been dried and fired their weight is reduced to approximately 18 pounds each.

It took more than 75,000 tejas to roof the buildings and outbuildings of the original Presidio quadrangle. That required 2,250,000 pounds  (1125 tons) of raw clay to be extracted and processed to make the tiles. To find out how and where all those tiles were fired, stay tuned for Part 3.

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

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.

Recent Research Leads to Re-analysis of Rare Religious Medal

by Michael Imwalle, Robert Hoover, and Anne Petersen

Drawing of the St. Vibiana medal made at the time of excavation.

In 1994, a small religious medal was recovered from the Northwest Corner of the Santa Barbara Presidio quadrangle during the Cal Poly San Luis Obispo Archaeological Field School. Dr. Robert Hoover directed the excavation, which was intended to identify the location of the bastion on the Presidio’s northwest corner. While the excavation did not result in identifying the former bastion location, it was successful in identifying a suite of two adobe rooms that were added to the north end of the west wing of the presidio quadrangle some time before 1795. Given the archaeological context of the find, and what appeared to be an inscription in Spanish, we initially assumed that the medal was probably deposited during the Spanish or Mexican period occupation of the Presidio.

The medal before restoration. Photo by Mike Imwalle.

After a preliminary cleaning of the medal, it was identified as a religious medal bearing the name and likeness of Santa Vibiana.  Saint Vibiana was a third century Christian martyr buried in catacombs in San Sisto on the outskirts of Rome near the Appian Way. Her burial vault was rediscovered during excavations of the site which were authorized by Pope Pius IX in 1853. The unopened sepulcher was sealed with a marble tablet bearing the Latin inscription “To the soul of the innocent and pure Vibiana, laid away on the day before the kalends of September [August 31].” A laurel emblem commonly used for early Christian martyrs was found at the end of the inscription. After several weeks, an investigation led to the canonization of Vibiana. Clearly the medal bearing the name “Santa Vibiana” postdated her canonization.

Mike Imwalle gently cleaning debris from the medal using a pick. Photo by Anne Petersen.

What does Pope Pius IX, the Appian Way, and a third century Christian martyr have to do with the Santa Barbara Presidio? That question was answered by the late art historian Dr. Norman Neuerburg when he revealed that the remains of St. Vibiana were once housed in the Presidio Chapel.  As it turns out, Bishop Thaddeus Amat was entrusted in 1854 with the bones of Vibiana, the marble slab, and a vial of blood from the tomb as relics for the Old Plaza Church in Los Angeles. Amat sailed from LeHavre, France, to New York, to Panama, and finally to San Francisco. Travelling on the coastal schooner, Powhatten, Amat’s journey to Los Angeles was interrupted by a sudden storm, forcing the ship into Santa Barbara harbor on December 2, 1854. The relics were temporarily placed in a special reliquary with a golden crown to the right of the Presidio Chapel altar. Later they were moved to Our Lady of Sorrows parish church where they resided until it was destroyed by fire in 1863. Miraculously, the relics survived the fire and were eventually moved to the old Parish Church in Los Angeles in 1868.

The St. Vibiana medal after cleaning. Photo By Mike Imwalle.

A recent inquiry by UCLA graduate researcher Vitaly Efimenkov led to the re-inspection of the inscription of the medal excavated at the Presidio in 1994. The medal was soaked in a bath of mild detergent in an ultra-sonic cleaner  and gently cleaned with wooden picks, dental picks, and tooth brushes.  After repeating the process for several days we were able to decipher considerably more of the inscription. Roughly translated the inscription on the front reads, “Saint Vibiana, Virgin and Martyr.”  And the back, “Oh Mary, conceived without sin, pray for us, we need your protection.” Amazingly, even some of the original gold plating began to re-emerge. Thank you, Vitaly, for instigating this process. I hope that your research sheds some light on why St. Vibiana’s remains ended up staying in Santa Barbara for almost fourteen years on the way to Los Angeles. Who could blame her, Santa Barbara is a special place!

Mike Imwalle is the archaeologist at SBTHP.  Robert Hoover is Professor Emeritus of Archaeology at Cal Poly San Luis Obispo and president of the board of  SBTHP.  Anne Petersen is Associate Director for Historical Resources at SBTHP. 

What’s Beneath our Feet! Using Geophysical Survey Techniques as an Archaeological Tool

By Michael Imwalle

Lucas Nichols collecting data with a Geoscan Research Resistance Meter near the Presidio aqueduct. Photo by Mike Imwalle.

SBTHP recently welcomed Dr. Lewis Somers of Geoscan Inc. to El Presidio de Santa Barbara State Historic Park to give a lecture and hands-on demonstration of geophysical survey techniques. The lecture was part of SBTHP’s Archaeology Month programming.  On Saturday, October 15th, 2011 Dr. Somers discussed the use of various geophysical survey methods including ground penetrating radar, resistance, and magnetics. He also discussed the effectiveness of the various techniques at other Spanish Colonial period sites.

Bob Guess, Lucas Nichols, David Jackson, and Ginny Guess look on as Dr. Lew Somers explains how the sensors on a Geoscan Research Fluxgate Gradiometer measure magnetic data. Photo by Mike Imwalle.

Following the lecture some of the attendees adjourned to the yard behind the comandancia for a hands-on demonstration of magnetometer survey and magnetic resistance survey. Both techniques employ the use of a grid system to collect data at predetermined spots across the site. Ropes representing the grid points are stretched across the site at one meter intervals. Correspondingly, each rope is marked with tape every meter. By walking along the ropes and timing the cadence of the instrument to record data at every meter marked on the rope, the data collected represents a grid of one meter squares across the site. While the magnetometer is carried just above the ground to collect data about the magnetic qualities of what is beneath the surface, the resistance meter consists of two probes inserted into the ground to measure electronic current as it passes through objects beneath the surface.

Bob Hoover outstanding in his field! Actually Bob is assisting with moving the survey ropes across the site. Note the intersection of two gridlines on Lot 72. Photo by Mike Imwalle.

The purpose for Dr. Somer’s visit to California was twofold. After the lecture at the Presidio, Dr. Somers packed up his equipment and hauled it over the pass to the Santa Inés Mission. He was contracted to survey the adobe apartments for neophytes formerly located south of the mission quadrangle. The survey was funded by the California Missions Foundation. On October 17th, 2011, SBTHP volunteers and staff assisted with establishing a one meter by one meter grid across an area measuring almost 200 meters by 200 meters. SBTHP Board President Bob Hoover, Santa Inés Mission Mills Steward Wayne Sherman, and volunteers Allison Lorber, Lucas Nichols, Arturo Ruelas and I assisted with moving the survey ropes across the site as Dr. Somers recorded the magnetic data.

Dr. Lew Somers collecting magnetic data with the Geoscan Research Fluxgate Gradiometer and the Santa Ines Mission property. Photo by Mike Imwalle.

Different techniques can provide varied results depending on a number of factors including the type of soil, the amount of iron in the soil, the amount of moisture in the soil, and the underlying geologic formation. Other factors such as the amount of “electronic noise” from metal fencing, underground, conduits, and overhead communications and power lines can also affect results. The best technique is the technique that provides the best results. The results may be partially determined by factors that can change like the amount of moisture in the soil.  Because the soil was very dry in October, Dr. Somers concluded that it was not practical to use resistance. He will return to the site in April 2012 to re-survey the same areas using resistance after the rainy season and be able to compare the results of the two techniques.

Volunteer Arturo Ruelas looking at a preliminary plot of the magnetic data from the area near the adobe apartments within the neophyte village at Santa Ines Mission. Photo by Mike Imwalle.

Geophysical survey is an extremely valuable tool for archaeologists for developing research designs, testing strategies, and resource management. Having an idea about what is under the ground before an excavation allows limited resources to be focused on areas where there is a high probability of encountering features. Knowing where buried features lay without having to excavate them allows interpretation of the site without damaging it.  It also provides information to archaeologists and planners to help avoid archeological resources during development projects and preserve them in situ for future generations of researchers.

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

The Button Hole: Part II

by Wayne Sherman

(Did you miss part 1? You can find it here.)

Photo by Mike Imwalle.

This past summer, students in SBTHP’s Presidio Archaeological Field School, a partnership with Cal Poly San Luis Obispo, found a Civil War-era button behind the Presidio Chapel. This button is known as a General Service button and is found on uniforms in all three branches of the Union Army. The raised mark in a depressed channel on the back of the button is a dead give away that this is a button manufactured during the war years 1861 to 1865 by the Waterbury Button Co. of Connecticut. It is a coat-sized button, as opposed to the smaller cuff-sized buttons, and most likely came off a frock coat or a sack coat; two styles worn by Infantry and Cavalry troops, respectively.

In terms of value, it can be assumed that Butterfield’ s and Cowan’s auction houses won’t be having a fist fight over it anytime soon, as it is worth about five dollars in dug condition to a Civil War collector. However, in terms of historical value to Santa Barbara’s legacy, it is a real gem. Very few American Civil War artifacts have been unearthed in Santa Barbara to date and this may be the first with definite evidence of dating to the period.

In the first post I alluded to how the button may have been lost, without completely identifying who the groups of men were that may have lost it. Considering there were millions of men wearing these buttons during the war (17,000 in California alone), we are quite lucky that after examining the historical record we can narrow our suspects down to about 400 possibilities.

The first two hundred “possibilities” arrived in January of 1862 in response to requests from local officials. Pablo de la Guerra had asked for a presence back around May of 1861 but was refused, as there weren’t enough troops to go around. In October of the same year, local Anglo officials petitioned for troops as they were concerned about the possibility of Californios and the Mexican population in the area having Southern sympathies. Companies H and I of the 2nd California Volunteer Infantry were sent to check the problem and by April realized that the case had been overstated. In April of 1862, Company H and I were sent north to Fort Humboldt and Fort Gaston to quell Indian insurrection in the area.

In December of 1863, one of the authors of the October 1861 request, District Attorney Charles E. Huse, wrote to General Wright that the native Californios were arming and receiving help from the French who were boasting that a French flag would soon be flying over Santa Barbara. Mr. Huse offered a building owned by himself to house the troops. The response was the posting of Company G of the 4th California Infantry in Santa Barbara from January of 1864 until November 1864.

Anyone of the above 300 men could have dropped that button, but since it was found in what was then considered the Hispanic part of town, I’m betting it came from a member of Company C of the California Native Cavalry Battalion recruited in Santa Barbara by Captain Antonio María de la Guerra in July of 1864. Recent drought had decimated the cattle industry and many a Ranchero was out of work, making it easy for the Captain to find good and able horsemen to fill his company. With names like de la Guerra (3), Pico (3), Cordero (5), Garcia (8), Gutierrez (2), Arellanes (2), Cota, Lara, Moreno, Valenzuela, Soto, and many more recognizable names of local Santa Barbara families on the roll, and living in the Presidio area during that period, it is not hard to believe that one of these native sons lost that button from his blue Union sack coat during, or even post-war.

We will never know who lost this simple little Civil War bauble that most Civil War enthusiasts would brush aside to consider the more rare or valuable item. I, for one, am extremely grateful that the archaeologist’s brush brought it to daylight. Common as it may be, just look at the wonderful tale it has unearthed for us about Santa Barbara’s Civil War history.

Wayne Sherman is SBTHP’s Santa Inés Mission Mills Steward and a Civil War re-enactor with the Fort Tejon Historical Association’s Civil War program. He portrays a Cavalry Trooper with Company a 2nd Massachusetts Volunteer Cavalry aka “The California Hundred.”

Join us at 10am on Friday November 11 at El Presidio de Santa Barbara State Historic Park for SBTHP’s Veteran’s Day ceremony. Wayne will be presenting a very special display of his collection of Civil War objects and archival material. For more information please call (805) 965-0093.

The Big Reveal: Archaeological Mystery Objects

Last week we posted three mystery objects excavated at El Presidio de Santa Bárbara State Historic Park, along with polls so you could guess the answers.   Below are the correct identifications of these objects.   How did you do?

Dried ink for calligraphy.  These small containers of dried ink can be wet with a brush, producing a black ink used for writing Japanese or Chinese characters. These objects were excavated from a trash pit associated with the early-twentieth-century occupation of the Presidio site by Japanese Americans.


Bale seal. Bales seals were in use throughout Europe going back to the medieval period to identify the content and quality of parcels, batches of textile, and bales of goods.  This bale seal was excavated from a trash pit associated with the comandante’s residence adjacent to the chapel site.


Dispenser for powdered Tabasco.  Marked with the company brand name on the bottom, this ceramic shaker shaped like a chili pepper was used to dispense a powdered form of the spicy condiment.  Tabasco brand products have been manufactured by the McIlhenny Company in Avery Island, Louisianna since 1868. Still in use in some areas of the Southern  United States, powdered Tabasco is not readily available on the market today, and this ceramic shaker is extremely rare.

What is it?: Day 3

Celebrate Archaeology Month and the 50th Anniversary of archaeological excavations at El Presidio de Santa Bárbara State Historic Park this Thursday October 13 with a lecture by archaeologists Bob Hoover and Mike Imwalle at the Presidio Chapel, 7:00pm.

Here’s your final Mystery Object, excavated at the Santa Barbara Presidio.  Can you guess what it is?  Take our poll and compare your answers with others!

Answers will be revealed during the lecture.  If you can’t make it, check the blog next week.  We’ll post the answers here too!