Seashells were considered to be very significant items in the pre-Hispanic world. For certain cultures they were as valuable as precious stones. They were used as jewelry, decoration for textiles, musical instruments, currency etc. In the Tlalocan-Tepantitla temple, located at the famous Mexican pyramids site “Teotihuacan”, as in many other sites, seashells were discovered in hundreds, probably serving as sacred offerings. Some were also decorated.
The seashells from Teotihuacan were buried for hundreds of years in a damp acidic soil. Therefore, the protein matrix that is embedded in the CaCO3 layered structure has solubilized almost completely. Moreover, CaCO3 structure itself has greatly degraded, as it naturally reacts with acids. Alcántara-García and Casanova-González indicated in their presentation that the shells “would crumble by the touch of a hand”. Mechanical cleaning was not a viable option in their state.
SEM image of an Archeological shell showing two mineral layers (aragonite) about to delaminate (photograph courtesy by the presenters. Has not been published yet)
The two researchers presented their initial trials in establishing a mass treatment procedure for the degraded, non-painted seashells. The procedure should be inexpensive, time efficient and on site, via controlled carbonation. They tested both artificially aged seashells and actual samples from the site. Firstly the shells were stabilized in a humidity chamber, then they were submerged into a limewater (Ca(OH)2) solution and were kept inside a sealed CO2 saturated atmosphere for controlled carbonation.
Before and after treatment, the samples were examined for changes in their properties: hardness and water absorption tests were performed as well as colour change assessment. The mineral structure was also analyzed by XRD and SEM. The preliminary results were encouraging. The hardness and porosity properties were improved and the colour change was minor. However, on the archeological samples, the CaCO3 which was formed by this process, accumulated as a superficial layer on top of the natural ones, and initially did not penetrate well. This new layer did not render enough stability to withstand handling and to hold the shells without them disintegrating.
My thoughts as a listener object conservator: Shells, much like bone or ivory, are created in biological processes but their composition is mainly inorganic. In cases of structural degradation of these materials, I am more familiar with consolidation treatments which involve diluted synthetic resins of various types. What I liked in this presentation was the shift in approach towards shells. Alcántara-García and Casanova-González presented an interesting new approach to restore the degraded shells which mostly lack protein matrix. As a mineralized, non-organic substance, they applied a treatment that is more common in stone conservation. This diffusion in materials, methods and thoughts between the different fields was very interesting for me.
(The presenters requested that I mention that the results of their research have not been published yet)
Hadas Seri, Object Conservator, Chemistry Conservation Laboratory for Organic and Metal Artifacts, The Israel Museum
Category: Research and Technical Studies
Posts on research, materials & techniques used in and by conservators
43rd Annual Meeting – RATS Session, May 15, "Polymer Coating Removal Nanosystems for Finely Controlled Cleaning of Cultural Heritage" by Piero Baglioni
I was certainly glad that I woke up in time for the first Research & Technical Studies talk of Friday morning’s session, which was presented by keynote speaker Dr. Peiro Baglioni. Dr. Baglioni is the Chair of Physical Chemistry at the University of Florence and CSGI (Consorzio Interuniversitario per lo Sviluppo dei Sistemi a Grande Interfase, or in English…Center for Colloids & Surface Science).
Dr. Baglioni discussed the systems that they have developed to clean synthetic coatings as well as dirt and grime from pictorial art surfaces. He started by discussing the Florence Flood of 1966, showing images of some of the resulting damage to cultural heritage, and explaining how new methods of conservation really developed as a result of this catastrophic event. Dr. Baglioni explained that his work has focused on searching for new scientific methods and materials for conservation treatment.
His talk then launched into a group of newly developed cleaning methods. This includes nanoparticles, micelles & microemulsions, and containers (gels). These systems can be used for cleaning dirt/grime from mural paintings and wood, as well as for polymer coating removal. Dr. Baglioni even mentioned paper deacidification applications. Some of this information can be found on the Nano for Art site and I would urge anyone interested to check this link out. Dr. Baglioni has also co-edited a book titled Nanoscience for the Conservation of Works of Art.
Dr. Baglioni put forth the question – why not just use solvents for cleaning? He explained that synthetic polymers have been popular for conservators since the 1960s, but can age poorly. He showed examples of poorly aged polymer coatings at the Mexican Mayapan site. Using traditional solvents and swabs in coating removal can cause the solubilized polymer to inadvertently be injected into cracks within the deteriorated art surface. Alternately, using microemulsions not only keeps the cleaning material on the art surface, but also has the added benefit of being less toxic for the conservator.
3 types of cleaning gels were discussed: 1) PVA/Borax hydroxide gels, 2) Hydrogels, and 3) Organogels. Dr. Baglioni explained that the PVA/Borax hydroxide gels could be used as a peeling gel, i.e. can be placed on a surface and then peeled off later. The hydrogels could be a carrying system for various solvents and solutions. They can also be cut into gel squares and even re-used. Impressive visible light, UV light, and SEM photos of surfaces at various stages of cleaning showed how effective yet safe these cleaning gels can be.
Personally, I would love to try out some of Dr. Baglioni’s cleaning materials! There are definitely applications for a wide range of art surfaces. The cleaning materials are trademarked, but I believe they are available commercially (does anyone know where to purchase them?). Dr. Baglioni has so much valuable information to share with the American conservation community. I’m sure I’m not the only one that wished that his talk could have gone on a bit longer so that he could go into more detail. It seems like this talk only covered the tip of the iceberg in regards to his research. Excellent way to start out the RATS session!
43rd Annual Meeting – RATS Session, May 15, "New Inorganic Consolidants for the Restoration Market: Results From Nanomatch EU Project" by Adriana Bernardi
Dr. Adriana Bernardi was the presenter for this co-authored talk. She is affiliated with Padua University, a senior researcher at CNR-ISAC (Institute of Atmospheric Sciences and Climate of the National Research Council of Italy), and head of the ISAC Unit of Padua. First, Dr. Barnardi explained that 13 partners from 7 European countries were involved in the Nanomatch project. This was a large-scale collaborative project with the aim of developing better consolidants for stone, wood, and glass artifacts. Discussions of wall painting consolidation were included as well. The developed consolidants had to be sustainable, react well with the substrate, and be safe to use. This talk discussed the testing and results of several new consolidants.
For stone and wood the class of consolidants that Dr. Barnardi described were calcium alkoxides. For glass, the consolidants were aluminum alkoxides (A18). Dr. Bernardi talked about the strategy for developing these consolidants. A mix of lab experimentation and field exposure was used in their development and testing. Mock-ups were made of wall paintings, wood, glass, and stone artifacts for testing purposes. Field tests were also done in several EU countries and Dr. Bernardi mentioned historical samples being tested as well.
The results of the Nanomatch Projcect were quite positive. There was too much detailed information to include everything in this blog post, but here are some of the highlights:
- Stone – developed consolidant had good workability and use, was comptablible with stone, and there was no color change.
- Wall painting – good workability and ease of use, good aesthetic results but decreased concentration needed for some colors.
- Wood – acid neutralization in alkoxide treated wood. The consolidant acts as an alkaline supply.
- Glass – consolidant A18 is highly compatible with glass (transparent, similar refractive index), good adhesion to glass, can penetrate cracks.
Dr. Bernardi showed videos during her presentation that demonstrated the use of the consolidants on stone, wood, and glass during Nanomatch training workshops. In conclusion, the newly developed limestone, wall painting, and glass consolidants all seemed effective as consolidating materials, while the wood “consolidant” was more effective in acid neutralization. If you’d like to know more about this project and the composition of the consolidants, visit the Nanomatch website for more information.
43rd Annual Meeting – Joint Painting Specialty Group and Research and Technical Studies Session, May 14, “Franz Kline’s Paintings: Black and White?“ by Zahira Veliz Bomford, Corina Rogge, and Maite Leal
Three works by Franz Kline in the collection of the Museum of Fine Arts, Houston were discussed with regard to their condition and construction: Wotan (1950), Orange and Black Wall (1959), and Corinthian II (1961). While the first two paintings exhibit alarming craquelure and flaking, the latter is in good condition. Rogge details the Museum’s investigation into the circumstances which lead to such differing states of preservation, presenting a clear, thoughtful look at Kline’s working methods and legacy.
Prior to this study, it was suspected that condition issues stemmed at least in part from the presence of zinc white, which Kline is known to have used; however, the causes of instability were not quite so “black and white.” The three aforementioned paintings were examined using a range of analytical methods, and an array of inherent vices were identified, including underbound paint, zinc/lead soaps, interaction with the gelatin sizing in the canvas, the thickness of paint layers, and the use of poor quality canvas. Kline also seems to have modified commercial paints.
It was found that Kline’s methods of layering paint and use of various materials was crucial to each painting’s relative (in)stability. It was suggested additionally that Woton’s integrity was compromised due at least in part to transportation. In the presentation, an animated map charted the painting’s transit, making the point of how excessively well traveled the work has been during its somewhat brief lifetime.
While treatment options for the paintings discussed were and are limited by inherent vice, the work undertaken to specify the various forces at play was remarkable: this talk above all highlighted the incredible ability we have today to begin to unravel the complexity of intertwined degradation mechanisms.
43rd Annual Meeting – “Investigating Softening and Dripping Paints in Oil Paintings Made Between 1952 and 2007” by Ida Antonia Tank Bronken and Jaap J. Boon, May 14
Issues encountered during analysis and treatment of contemporary artworks by conservation scientists, conservators, and other professionals have been brought into the limelight during recent years. Both in the United States and throughout the world, contemporary art collections have introduced new concerns regarding the use of modern materials, artists’ intent, and so on. Even the modern use of materials such as oil paints have demonstrated conservation issues. During this presentation, Bronken described her team’s research into oil paintings (created after 1950) which have exhibited softening and dripping media. The team’s research was conducted on works produced by Jean-Paul Riopelle (Canadian, 1923-2002), Pierre Soulages (French, b. 1919), Georges Matthieu (French, 1921-2012), Paul-Émile Borduas (Canadian, 1905-1960), Frank Van Hemert (Dutch, b. 1956), Paul Walls (Irish, b. 1965), Jonathan Meese (German, b. 1970), and Tal R (Danish, b. 1967).
Softened paint shows decreased surface gloss in normal light and drip material fluoresces in ultraviolet light (sometimes misinterpreted as fluorescing varnish). Softening/dripping impasto and thickly applied paints are easier to identify, but analysis has demonstrated the presence of softening in thinner paint layers as well. Possible causes of this phenomenon are the use of semi-drying oils in recent decades and the development of fatty acids in paint. In their abstract, the authors mention: “There is ample evidence from a number of paints studied by mass spectrometry that the exudates are rich in polar fractions with triglycerides with moieties of mid-chain oxygen-functionalised stearic acids and azelaic acids . . . observations led to the hypothesis that exudation is caused by a loss or absence of anchor sites for the acidic fractions that develop over time.”1
Lead II acetate and europium II acetate were tested by brush and gel application. These compounds treated the softening and dripping oil paint at the molecular level by penetrating into the sample to create carboxylates and forming a hard crust on the paint surface. Brush application was determined to be the most effective method. At this time, the only disadvantage appears to be the lack of reversibility.
About the Speakers
Ida Antonia Tank Bronken, Touring Exhibitions Coordinator, The National Museum, Norway
Bronken graduated from the University of Oslo with a Candidata Magisterii in Fine Art Conservation (2002) and a Masters in Conservation (2009). Bronken has been working for the Touring Exhibitions Department at the National Museum of Art, Architecture and Design in Norway since 2011. Her main interests are collection management and chemical change in modern paint. Bronken has cooperated with Boon since 2007 on different studies on softening and dripping paint, and has contributed to four papers since 2013 about dripping paint (currently at different stages of publication and review).2
Jaap J. Boon, JAAP Enterprise for Art Scientific Studies
Boon, PhD was trained in Geology and Chemistry at the Universities of Amsterdam, Utrecht and Delft Technical University (1978). He became Head of Molecular Physics at the FOM Institute for Atomic and Molecular Physics (1987) and Professor of Molecular Palaeobotany at the University of Amsterdam (1988). His first survey studies on painting materials and traditional paints were performed in 1991, which resulted in collaborative research with Tate Gallery London, the Rijksmuseum in Amsterdam, the Limburg Conservation Studio (SRAL) in Maastricht and EU supported development projects. His research focus changed gradually from identification of constituents towards chemical microscopy and spectroscopic imaging of pigments, binding media and their interactions in paintings. Boon was Professor of Analytical Mass Spectrometry in the University of Amsterdam (2003-2009) and is presently author/coauthor of about 400 research papers and supervised 33 PhD theses. Boon received the KNAW Gilles Holst Gold Medal for his innovative work at the cross roads of chemistry and physics in 2007.3
1 Bronken, I., & Boon J. J. (2015). Investigating Softening and Dripping Paints in Oil Paintings Made Between 1952 and 2007 [Abstract]. AIC Annual Meeting 2015 Abstracts, 81-82.
2 Bronken, I. (2015). Ida Bronken – AIC’s 43rd Annual Meeting [SCHED Speakers]. Retrieved from https://aics43rdannualmeeting2015.sched.org/speaker/ida_antonia_tank_bronken.1t1j0ku0
3 Boon, J. J. (2015). Jaap J. Boon – AIC’s 43rd Annual Meeting [SCHED Speakers]. Retrieved from https://aics43rdannualmeeting2015.sched.org/artist/boon1
43rd Annual Meeting – Object Session, 16 May 2015, “Ivory: Recent Advances in its Identification and Stringent Regulation" by Stephanie Hornbeck
Stephanie Hornbeck wrapped up the morning OSG session with her talk, “Ivory: Recent Advances in its Identification and Stringent Regulation.” She set the stage by noting how international and U.S. laws were strengthened in 2014 to combat the rise in ivory trafficking, drawing the connection to conservators since we may be involved in the identification and sampling of ivory materials. It is important for us to be aware of the methods to identify ivory and of the new regulations that apply to it.
Stephanie presented some history about ivory and its use, including a detailed description on what ivory is and how it is formed. Stephanie carefully outlined the diagnostic features for identifying different types of ivory and included a host of images to illustrate her points along the way. Some excellent resources to help with this include Stephanie’s web article for the National Museum of African Art and the Fish and Wildlife Services (FWS) website, including this page on identification. A point that Stephanie drove home is how critical it is to have comparative data when attempting to identify and unknown specimen. Photographs of morphological features and known reference material are essential tools to use. An additional aid is the use of UV light as a screening tool to classify the unknown as animal versus vegetal or synthetic. Animal ivories will fluoresce blue-white due to the presence of apatite, while other materials are likely to absorb or produce yellow or orange. Stephanie reminded the audience that the presence of Schreger lines is indicative of Proboscidean ivory, and the angle of the lines can help distinguish between mammoth and mastodon versus elephant. However, she also pointed out that the angle of the lines is variable depending on where along the tusk the lines are being examined. Beyond these visual tests, Stephanie also outlined analytical methods that require sampling. These included FTIR and DNA for identification, as well as isotope analysis, bomb-curve radiocarbon analysis, and the potential of measuring water ad/absorption as methods for possible dating.
From here, Stephanie shifted gears to talk about the ivory trade and new international, federal, and state regulations. She pointed out that the US is the second largest consumer of ivory behind China and that the ivory trade is often a cover for other illicit trade. Although ivory was already a highly regulated material since the 1976 Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), these facts, along with the rapidly diminishing population levels of the elephant due to rampant poaching, have led to newer, tighter regulations. After an outline of the various laws and regulation that affect ivory, Stephanie explained that it is now illegal to buy or sell ivory of any age. Only well documented works that can prove a date of more than 100 years and ownership before 1977 can enter the US. The new requirements ask for species-specific identification and specific dating. These regulations are problematic because identifying and dating artifacts to those levels is difficult, if not impossible. The FWS has provided useful information on the new regulations here.
Because of time constraints, Stephanie was not able to fully delve into the implications for traveling exhibitions. She skipped over a case study in which documented ancient ivories owned by the Bolton Museum in Bolton, England were delayed at the Miami International Airport for four days in a tropical environment where climate controls were unknown. Following the new 2014 regulations, the local FWS agent wanted species specific identification of the ancient ivories, which was not readily proven in the existing documentation. That level of identification is also not possible to obtain without destructive analysis. Although ancient worked ivories should have been allowed as part of a traveling exhibition, and CITES permits were provided, the entry into the US was nevertheless delayed at great risk to cultural artifacts. For this reason, coupled with her long-standing research interest in ivory, Stephanie has joined a sub-committee to help develop an AIC position paper on the subject.
N.B. For information on the changes in regulations download: Hornbeck, S. 2016. “Ivory: identification and regulation of a precious material”. Washington D.C.: Smithsonian National Museum of African Art. available via the AIC wiki.
43rd Annual Meeting – Research and Technical Studies, May 15, “Parylene Treatment for Book/Paper Strengthening” by John Baty
In the 1990s there was a pioneering study on the use of parylene to strengthen brittle book paper performed by Don Etherington, David Grattan, and Bruce Humphrey. Ultimately their research did demonstrate that parylene strengthened weak, brittle paper, but several concerns regarding the material’s long term effects were raised; such as reversibility and the uncertainty of its aging properties. John Baty and his colleagues at the Heritage Science for Conservation Research Center at Johns Hopkins University, sought to reexamine the potential for using parylene to strengthen brittle paper, given the improved scientific instruments and analysis methods available today. Their research sought to answer five primary research questions: does parylene strengthen paper, what is the permanence of its effect, what are the side effects, how can parylene treatment be scaled up, and how can it be reversed. Currently they have answered the first two and are conducting ongoing research.
Parylene is applied to brittle books by using a chamber that draws a vacuum and essentially pulls sublimated parylene through the system. The amount of parylene dimer that is added to the chamber directly correlates to the thickness of the deposited film. Previous research had not optimized the amount of parylene needed to achieve a desirable film layer, so this was a primary goal for Baty and his colleagues. The success of the treatment was evaluated using three mechanical paper strength tests: tensile testing, the MIT fold endurance test, and the Elmendorf tear test.
Baty and his team found that using 3 grams of parylene was sufficient to strengthen brittle paper to the point that it behaved similarly to modern wood pulp paper and only imparted a smoother appearance to its surface. 5 grams of the dimer was too much and conservators inspecting the pages concluded that the paper had a more “plasticky” and stiff feel to it. The three mechanical tests did indicate that the brittle paper samples were strengthened with the addition of a parylene coating, but there are still questions regarding this treatment’s reversibility and side effects that remain to be answered by Baty and his team in subsequent research.
42nd Annual Meeting – Research and Technical Studies (RATS) Session, May 29, "Unwrapping Layers in Historic Artworks: Virtual Cross-Sections with Pump-Probe Microscopy" by Tana Villafana
For the last few years, Ms. Villafana and her co-authors have been refining a new microscopy technique for conservation to create “virtual” non-destructive cross-sections. This is a very exciting development for our field, particularly for those of us working with materials–such as works of art on paper–that don’t typically allow for sampling. And for paintings conservators more accustomed to taking traditional cross-sections, this technique has promise for in-situ analysis of paint layers through varnish.
To summarize, the virtual cross-section image is created using pump–probe microscopy, a non-linear optical microscopy technique developed for the biomedical field, which allows non-invasive detection of biological pigments indicative of skin cancer. Because skin tissue is highly scattering, this technique was developed to be inherently confocal, meaning that the signal is generated only at the focal point, creating less scattering, and less spectral noise. The approach is naturally suited to the highly scattering pigments, binders, and supports making up materials of cultural heritage. However, the complexity of art objects render the technique more difficult to apply.
Pump–probe microscopy achieves high resolution in three dimensions with a maximum image area of up to 1mm square. The penetrating depth ultimately depends on the material composition of the object under study. The technique is typically operated at two wavelengths: 810nm and 720nm and modulated to create a series of images at different inter-pulse delays. These images can then be colored according to the molecular composition of the specific material and stacked to create a 3D rendering.
With this presentation, Ms. Villafana shared case studies illustrating ongoing research into cultural heritage materials using pump–probe microscopy. The first project investigates applications of pump–probe on paper substrates bearing coatings of lapis lazuli pigment. With this technique, it is possible to produce an image illustrating the physical structure and condition of paper fibers underlying the paint layer. She observes that the pigment particles cluster around the fibers, as seen in the slide below. She is interested in further investigating the natural heterogeneity of lapis lazuli crystals, noting that samples from different parts of the world exhibit different delay behaviors. She plans to complement her pump–probe analysis of lapis lazuli pigments with SEM-EDS, Raman, and FTIR.
Villafana also presented on preliminary research using pump–probe to investigate historical methods of pottery manufacture. After finding that pump–probe delays of hematite are dependent on firing temperature, Ms. Villafana started using mock-up clay bodies fired under different conditions (Oxidized at 1800F and 2300F/Reduced at 1800F and 2300F) to examine the difference in delay behaviors from the exterior to the interior of fired clay. She has found that higher temperatures and oxidation both result in shorter lifetimes. Further study will focus on phase change and particle size.
I quite curious to see how this technique develops in the near future. Will pump-probe (or something like it) be able to replace traditional cross section techniques within the next 5 to 10 years? What other techniques are being developed out there that might be able to achieve similar results?
See the following two links for more information:
Villafana, et al., full-text PDF of recent research published in The Proceedings of the National Academy of Sciences of the United States of America
Article about Pump-Probe Microscopy in Science News, from Science, AAAS
42nd Annual Meeting – Joint Session: Objects + Research & Technical Studies, May 30, “Coping with Arsenic-Based Pesticides on Textile Collections” by Jae Anderson and Martina Dawley
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.
42nd Annual Meeting – Research and Technical Studies, May 29, "An Examination of Light-Induced Color Change in Anoxia and Hypoxia using the Microfading Tester " by Vincent Beltran, Jim Druzik, Andrew Lerwill, and Christel Pesme
Vincent Beltran from the Getty Conservation Institute presented this talk in the Research and Technical Studies session. The study presented examined the effects of anoxia and hypoxia on light-induced color change in a sample set containing a variety of materials. The goal was to examine the use of these environments in storage and exhibits as part of an effort to improve the experience for visitors viewing light-sensitive items.
The talk was organized into four parts: “Introduction,” “Experimental Method,” “Microfader Results,” and “Comparison to Lightbox Study.”
In the introduction, Beltran reviewed traditional practices to mitigate the damaging qualities of light. For example: reduce light levels, limit exposure time, rotate exhibit items, and store items in the dark. He then provided an overview of the photo-oxidation process, and the theories behind the use of anoxic and hypoxic environments for storage.
A 2012 study of 125 colorants exposed in a halogen lightbox for 17.5 MLux hours at 22° C, 40% RH with oxygen levels at <10 ppm indicated that 90% of these items studied showed reduced color change as compared to the same items stored in air. To the authors, the logical extension of this study was to transfer the test to the microfading tester and compare the results.
The design of the lightbox for the microfading tester study involved a xenon light projecting through ¼” starfire glass to items on a sample stand. Light was reflected to a spectrometer located above the glass. A ½ cm gap existed between the samples and the glass. The microfader was located above the case while the colorants were inside the case. The colorants consisted of 3 blue wool, 4 organic dyes, 2 leaves, 1 grass, 5 gouaches, 1 watercolor with prussian blue, 1 Kremer Prussian Blue, and 1 Crystal Violet. The colorants were exposed for 5 MLux hours in air, anoxia (<200 ppm oxygen), and hypoxia (1% and 5% oxygen). Reflectance spectra were obtained and combined for a color change plot.
The results of the microfading tester study showed that for the most part color change in air is higher than that in anoxia. Anoxic environments seemed to be generally equivalent to the 1% oxygen environments. A few colorants exhibited a slightly decreased change in the 1% environment but Beltran indicated that these results were inconclusive. A few exhibited increased change in the 1%. Environments with 5% oxygen tended to exhibit more change than anoxic or 1% but generally not as much change as found in air. The exception to this is Prussian blue, which shows the opposite behavior – an air environment showed the least change, 5% followed, and 1% and anoxic showed the most change. Overall, the results showed that 12 of the 18 colorants exhibited greater change in air while only one (Prussian blue) exhibited the greatest change in anoxia. Generally, hypoxic environments exhibited less change than air.
Beltran then presented a comparison between the 2012 study and the more recent microfader study. The main differences in the studies were as follows:
Study Component: Microfader Lightbox
Light Source: Xenon Halogen
Exposure level: 5 MLux 0.01 MLux
Exposure time: 3.5 hours 1750 hours
Exposure type: Continuous Start/End
Area exposed: 4 mm spot Broad exposure
In general, the color change with the lightbox test was higher than that seen with the microfader, though some samples showed changes which were roughly equivalent. Most items showed similar behavior between the two techniques but the lightbox displayed increased change. The differences in the studies were typically within one blue wool step, and the study was able to consistently classify relative color change between the two techniques. However, Beltran stated that there is reciprocity failure between the two studies.
Future goals of this project are to repeat the analysis with more samples, examine the effect on reciprocity for the microfading tester at reduced light intensity, and study the color change in various RH and temperature levels.
Questions were as follows:
Q: In cases where the microfading tester and lightbox didn’t agree, is the lightbox the more reliable?
A: In general, lower light exposure tends to be closer to what you’d get with the microfading tester but that doesn’t mean reciprocity is holding.
Q: Has the microfading tester been tried with a halogen bulb?
A: No, they tried to modify a halogen source but it didn’t do much.
Q: Were control samples used?
A: No, they were not..