Madeleine and Nancy presented a very interesting talk that shared their experiences using cold temperatures to achieve a specific treatment goal. Nancy began by introducing the object, a Lakota Winter Count. The object is one of a type of pictorial calendars that depict the history of the community and serve as a counting device. A historian would have been in charge of the count, naming years for remarkable events related to astronomy, the environment, or culture. Tribal keepers knew the name of the years, helping them to recall the oral history of the community.
The Lakota Winter Count that inspired this talk is from the Heard Museum in Phoenix, Arizona. At some point in the past, it had been folded so that the pictograph surface faced out. The interior surface had become stuck to itself, preventing the unfolding of the object. As the Heard Museum does not currently have a permanent conservation staff, the object was brought to the Arizona State Museum for treatment.
The primary goal of treatment was to unfold the count, enabling the viewer to see all of the pictographs at the same time. Additionally, there is bleeding, mold, darkening, and tears on the support. There was no history of fabrication or provenance associated with the object so the Arizona conservation team undertook documentation and investigation.
There are 121 pictographs on the non-coated side of the support that documents the years 1799 to 1918. The outlines are drawn in graphite and the limited additional pallette is consistent with other winter counts. These include two browns, a bright pink pastel, and blue and orange colored pencils. Specifically, the Heard winter count is very similar to a Long Soldier Winter Count at the NMAI. Sometimes, duplicates of counts were made for use or for sale, which could explain the similarities of the two pieces that cover roughly the same period. The Heard count is likely from a similar region in North Dakota.
The object was analyzed and the support was determined to be a piece of commercial oilcloth. FTIR showed the oilcloth coating is linseed oil and shellac. Fiber samples taken indicate that the fabric is cotton. This is consistent with commercial oilcloth produced in the late 19th, early 20th century; during this time period, commercial products began to replace local materials. Maker’s marks on the oilcloth identify the manufacturing company and Nancy and Madeleine shared contemporary advertisements, which demonstrated the prevalence of the product in the average household. The mark gives a terminus post quem of after 1901.
The fusing of the oil cloth to itself was likely due to ambient heat. A 1-2 cm opening along the edge was the maximum access before treatment. Dave Smith, conservation scientist at Arizona, was able to determine the glass transition period of the oilcloth coating is approximately 31⁰C. The average temperature in Arizona exceeds this from April to October, so the environment could have caused the shifting in the structure of the materials that led to the current sticking.
Madeleine undertook testing to explore options for opening the count. Organic solvents were not effective as the coating is cross-linked and now impervious. At this point, it was clear that whatever treatment was applied would be time consuming and invasive. The conservators asked the curators how crucial the treatment was to the object; however, the curators said that the current condition was fundamentally comprising the interpretation of the object as the chronological reading of the object was disrupted.
Knowing this, the conservators went back to the drawing board. Dave suggested considering cold temperatures, because polymers are long chain molecules whose movements are highly linked to temperature. If the temperature is below the Tg, then the polymers can no longer stretch and instead cleave, allowing for the two sides to be separated. Conservators tried compressed cooled CO2 gas, which was not effective. Similarly, overall freezing works at first, but the object warmed up too quickly for this to be viable for treating the whole object. Next, they used a Peltier cooler to apply repeated cold in a smaller area. The team worked to retrofit a USB beverage chiller to be able to consistently apply a 5⁰C. This system was used by applying the cooling plate to oilcloth surface for three minutes, then lifting the device so that Madeleine could use a stainless steel spatula to cleave small sections of the cloth from the opposite surface. She continued in this way for three months, working on the project for portions of each day.
After the cloth was opened, treatment turned to the tears, some of which appear to be linked to earlier attempts to force open the oilcloth. Stitching the tears was not viable because there was no safe place to secure the tears given the nature of the oilcloth. Adhesive backings also were not expected to be successful, as they would likely curl away from the coated surface over time. Instead, Madeleine found that by applying granules of textile welding powder to individual warps and wefts, she could control her mends and allow for a degree of reversibility. This process required four steps: relax the creases using Gortex, Dartex, and weights; pull misaligned fibers back into place; reweave fibers where possible; and, apply the granules of adhesive. The granules were heated in situ to a temperature at which they began to soften but did not completely solubilize, so that individual granules could then be mechanically removed if necessary. In some places, a secondary support was added where there were not enough wefts or warps. Small pieces of Remay were torn to the right shape, toned with dilute acrylics, dusted with the welding powder, and heated between silicone release paper in place.
Thus, the treatment presented benefited from the use of both low heat and cold temperatures. It was highly time intensive; however, this was considered justifiable as the object was a special project. The speakers also encouraged conservators to consider the use of cold for other treatment applications, as it seems to be underexplored when compared to higher temperatures.
After the presentation, one question was asked:
- Q: Why did they not just heat the oilcloth coating to past the glass transition temperature? A: Doing this would likely have caused the cloth to become more sticky, more bonder, and more flexible. When the polymers are cold, they want to break due to the brittleness. The weakest point of contact in this case was with the other side, so cleaving the polymers facilitated the treatment goal.
This post was written from my personal notes, which may contain errors or inaccurately represent the author’s original intentions.