Presenters:
Jae Anderson – MS candidate, Materials Science and Engineering, University of Arizona, member of Navajo tribe.
Martina Dawley – PhD candidate, American Indian Studies, and Assistant Curator for American Indian Relations, Arizona State Museum, member Hualapai and Navajo tribes.
Nancy Odegaard – Conservator Professor, Arizona State Museum.
Nancy Odegaard began by introducing this project to develop guidelines for the removal of arsenic from textiles utilizing a portable X-ray fluorescence analyzer (pXRF). She explained that a number of different forms of arsenic have historically been used on the collection at the Arizona State Museum (ASM). For this project, the team chose to focus on Navajo textiles due to the consistency in their materials and construction. In addition, they were able to consult with local Navajo (or Diné) weavers. Martina Dawley and Jae Anderson, who both worked in the ASM conservation lab on the project, presented the remainder of the talk.
Martina described her role in carrying out a survey of the Navajo textile collection, which includes blankets, rugs, and looms. She researched provenance information, produced documentation, and performed XRF analysis on each piece. One of the questions raised during the project was whether the rolled textiles could be analyzed with the pXRF while on the roll or if they had to be unrolled flat first. Interestingly, Martina noticed that the first reading on an object was diagnostic of the remaining readings on that object overall. If the first reading for arsenic was below 100ppm, most of the other readings were also below this level, and the corresponding trend was true if the first reading was greater than 100ppm. Therefore, for textiles with a lower initial reading, analysis was continued on the roll, meanwhile textiles were unrolled for more thorough testing if a higher-level initial reading was found. In the end, 17% of the textiles she tested were found to have levels at or above 100ppm, and the majority of these pieces (69%) were from the 1800’s. Forty-seven percent had less than 100ppm of arsenic, and 36% were found to have no arsenic.
Jae explained the experimental portion of the project in which the pXRF was calibrated and textile-washing methods were tested. First he described two inorganic arsenic species – arsenite, As(III), and arsenate, As(V). Arsenite is more toxic and is commonly in the forms arsenic trioxide and sodium arsenite. It can convert to arsenate by oxidation in wet conditions. For calibration and experimental testing, Jae wetted cotton and wool fabric samples with arsenite solutions of varying concentrations. Another variable tested was application method; he applied the arsenic solutions by droplet, dipping, and spraying, of which the latter two are traditional arsenic-pesticide application methods. During this step, he noticed the wool curled because of its hydroscopic nature, so he altered the experiment to utilize Chimayo hand-woven wool. He also added a surfactant to help with wetting properties and food coloring as a visual cue to see that solutions were applied evenly. Each fabric sample was analyzed five times, both wet and dry, with the pXRF in order to create a calibration curve.
Next, the fabric samples were washed in deionized water, and various conditional effects were tested, including temperature, pH, time, and agitation. The samples were again analyzed with pXRF and the results compared. Increasing the temperature and altering the pH of the wash water were found to have no effect on arsenic removal. The greatest arsenic removal overall occurred within the first 10 minutes of washing, and agitation caused a substantial increase in the effectiveness within the first five minutes. Therefore, the preliminary guidelines were washing for 10 minutes, at a neutral pH, with agitation, at room temperature.
After washing the fabric test samples, the team attempted to analyze the post-wash water with a paper indicator, however this test was not sensitive enough, nor did it indicate concentration. Inductively coupled plasma optical emission spectroscopy (ICP-OES) has the potential to quantify the levels of arsenic transferred to the wash water, and Jae noted that they are beginning to utilize this technique. Nevertheless, the post-wash water was found to contain less than 5 ppm arsenic, so it could be disposed of down the drain, according to municipal and federal regulations.
During the next phase of the experiment, three Navajo textiles were washed according to the preliminary guidelines. (Note that prior to washing, the textiles were documented, analyzed using pXRF, and their dyes tested for colorfastness.) After washing the first textile and finding the results did not correlate with their experimental data, the procedure was altered – the volume of wash water was calculated based on the experimental tests. The second textile washed was initially found to have high levels of arsenic (greater than 100ppm). Good results were achieved, with 96% of the arsenic removed and only minor dye bleeding. The third textile initially had low levels of arsenic (less than 100ppm) and less arsenic was removed during washing. Therefore, better results were achieved (i.e. greater arsenic removal was possible) when arsenic was initially present in higher quantities.
Overall the project surveyed 600 Navajo textiles and identified time-period and collector-dependent trends in arsenic concentrations. The team developed a cleaning protocol in which 95% of arsenic could be removed in high-arsenic contaminated textiles but with less effective results in lower arsenic containing textiles. The mass of the textile, the volume of wash water, as well as agitation and wash time (up to a point), were found to have an effect on results.
Several questions were posed in response to the presentation. One audience member wanted to know about the health and safety outcome of washing – could the textiles now be handled safely without gloves? Jae explained that the results would have to be evaluated by a medical toxicologist. Another attendee was interested to know if this technique could be used on a collection of fragile Egyptian textile fragments with a known history of pesticide treatment. Nancy replied that arsenic can be removed with washing, but the stability of the textile and its ability to withstand washing is a separate issue. Finally, someone asked if the arsenic species, arsenite vs. arsenate, could be identified on the textiles? Jae explained that the two forms are too similar to be distinguished here.
I look forward to hearing more results from this team as they continue exploring new experimental procedures and further developing arsenic removal techniques. Learn more about the ASM’s Preservation Division here.
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AIC Blog Archives: Conservators Converse
Former Blog of the American Institute for Conservation