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Learning from the Past at Tuzigoot National Monument

March 25th, 2013

Learning from the Past at Tuzigoot National Monument: Early Conservation Efforts Gone Awry

 Sara Kerfoot

            Conservation is exciting. A properly trained conservator has the chance to stop the deterioration of artifacts and structures. This talent allows both conservators and archaeologists to discover human stories. Not only are stories being rediscovered but also artifacts are put in a state of preservation. By preserving an artifact or site, future generations have an opportunity to share in the story and to use future technologies to uncover more of the past.

The art of conservation, however, has not been perfected. Each object that has been put under a conservator’s protection is part of a learning curve of discovery. This means that with time and practice, conservation efforts become more productive in their goal through the trial and error of past conservation projects. This is not to say that conservators are blindly experimenting with solvents and tape in order to restore something to its original prestige. In fact, it is saying quite the opposite. The whole mentality of conservation has undergone quite the change in maturity since its origins. The point is not that these people were bad conservators to begin with, in fact, it can be quite sure that these people had the best intentions for the artifacts. It is with time that conservation efforts can be seen as positive or negative, despite the scientific effort that went into the original conservation project (Godfrey 1990; Jakes 1992). Efforts now, are broadly to preserve. Restoration has become less popular because it is impossible to understand the intentions of the original crafter (Caple 2003; Sease 1996). True, some original efforts were “bad,” but with these original follies, it is possible to understand the limitations of various conservation projects.

A valuable example in the growth of conservation efforts can be seen at Tuzigoot National Monument, located in Cottonwood, Arizona. Louis R. Caywood and Edward H. Spicer excavated the pueblo in 1933-1934 (Caywood 1935). They were graduate students at the time of the excavation, and workers from the Federal Emergency Relief Agency’s Civil Works Administration assisted them (Arizona Ruins 2012).  This was a massive project, once the work was done and the reports turned in, Franklin D. Roosevelt allowed Tuzigoot Ruins to be a U.S. National Monument on July 25, 1939 (NPS 2013).

After excavation, the monument was left exposed. The pueblo is predominately made from limestone, the mortar that holds it together is from river sediments, ash and other natural binding materials. Without the Sinagua (peoples that lived at Tuzigoot) to do annual maintenance on the pueblo, it was understood that weathering would soon erode this structure away. So in order to counter-balance nature, workers covered the mortar with Portland cement in order to hold the monument together.

Portland cement was an incredibly popular preservationist tool used all throughout the American Southwest in the 1920s. This was because it was “cheap, easy to mix and apply, could be tinted to match any color and is incredibly strong” (Guebard 2013). Preservationists of the time were very concerned about the wall stability, so they did what they thought was best to conserve the integrity of the wall. The issue is that today, with the knowledge of what long-term effects negatively impact Tuzigoot’s walls, the Portland cement is being removed.

The archaeologists at the park have learned that Portland cement is negatively impacting Tuzigoot for a number of reasons. Some of them are: differential erosion, mineral formation and water retention (Guebard 2013).

Portland cement is considerably stronger than the original, non-synthetic mortar. This causes differential erosion. The cement is much harder than the sediment mortar, so when windblown sediments blow across the monument, it erodes the softer materials and leaves the Portland cement as is. Since some of the structure is being eroded away and other parts are staying intact, this leaves the structural integrity at risk. The softer parts of the pueblo can become voids within the larger context of the additives; this can cause a collapse. These are effects that preservationists can see today, so in order to fix the issue the Portland cement is slowly being chipped away. In place of that particular synthetic mortar, they now mix 10 percent Portland cement with 90 percent sand which creates an even erosion pattern (Guebard 2013).

 

worker patching

(NPS worker removing original Portland cement)

            Another issue with the harder Portland cement is that it does not “breathe” as well as natural materials. This is an issue because when it rains, water stays retained in the walls rather than drying quickly. Moisture inside the walls can deteriorate the interior structures; it is much better for the structure if after a rain storm the water evaporates quickly. When stones remain wet, they are more likely to succumb “to cracking and breakage caused by expansion/contraction, freezing/thawing and mineral depletion (continued wet/dry cycles may leach minerals from stone, causing them to become weak)” (Guebard 2013). Another issue is that Portland cement has soluble minerals in the mixture that can hurt the monument. They include: chlorides, carbonates, and nitrates. This has the potential to deteriorate the softer stones used in the structure. Once again, these are impacts that are only seen with time. Conservators’ efforts of the past are being dealt with currently in order to maintain structural integrity (Guebard 2013).

There are other issues that Portland cement brings, such as negatively reacting with UV light and changing it’s aesthetic make-up to non-natural colors such as purples and blacks, but this is not affecting the structural integrity of the wall so it will not be addressed here. Conservators have learned a lot through trial and error, Tuzigoot’s Portland cement issue is a prime example of that. In order to deal with the situation, Tuzigoot’s head archaeologist, Matt Guebard says, “When possible, we use only natural materials to avoid unintended interactions between synthetic materials and the environment” (Guebard 2013).

Conservation is a relatively new field, and it is still learning. There may be mistakes along the way, but publishing projects allows for a group learning curve to be achieved. With each project, professionals are getting closer to permanently maintaining features of past cultural heritage.  Conservators must thoroughly be aware of past conservation efforts in order to grow as a profession.

References: 

Arizona Ruins. 2012. Tuzigoot, Hatalacva & Bridgeport. <http://www.arizonaruins.com/tuzigoot/tuzigoot.html>. Accessed 3 March 2013.

Caple, C., 2003, Chapter 4.2: History of Conservation. In: Conservation Skills: Judgment, Method and Decision Making, pp. 50-58.

Caywood, Louis R, and Edward H. Spicer. 1935. TUZIGOOT-The Excavation and Repair of a Ruin on the Verde River near Clarkdale, Arizona. U.S. Department of the Interior. < http://www.nps.gov/history/history/online_books/berkeley/caywood-spicer/intro.htm>. Accessed 3 March 2013.

Godfrey, I., and N. Smith. 1990. Conservation of Degraded Rope from Maritime Archaeological Sites. In: AICCM Bulletin, Vol 16, No 3, pp. 93-108.

Guebard, Matt. February 2013. Chief of Resource Management, Park Archeologist at: Montezuma Castle National Monument and Tuzigoot National Monument. Email Correspondence.

Jakes, K. and J. Mitchell. 1992. The Recovery and Drying of Textiles from A Deep Ocean Historic Shipwreck. In: Journal of the American Institute for Conservation, Vol 31, No 3, pp. 343-353. Electronic Resource.

NPS. 2013. Tuzigoot National Monument. Department of the Interior. <http://www.nps.gov/tuzi/index.htm>. Accessed 3 March 2013.

Sease, C. 1996. A Short History of Archaeological Conservation. In: Roy, A. and Smith, P. (eds.) Archaeological Conservation and its Consequences, pp. 157-161).

General Conservation

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