Research and Technical Studies – Page 11 – AIC Blog Archives: Conservators Converse

39th Annual Meeting – Architecture/Research and Technical Studies Joint Session, June 3, Consideration of Infrastructure in the Assessment of Historic Fountains by Thomas J. Podnar

Thomas J. Podnar opened with a picture of an anonymous fountain to illustrate the beauty of these structures and their ability to bring beasts together (displayed by horses drinking from the fountain). The talk consisted of three case studies which are summarized below.

The Probasco Fountain in Cincinnati, Ohio (c. 1887) was the subject of the first case. The fountain consists of Quincy granite with a polished bowl and a bronze top. The fountain was located precariously close to an existing roadway, and Podnar was hired to evaluate the condition of the fountain and explore the feasibility of moving it to a safer location. During an investigation of the interior cavity, he found a water main running through the chamber and an electrical box, which was added for display lights. Research of historic photographs revealed that the water display had been diminished and that it was missing elements such as drinking cups. In the end the city decided that it was cheaper to move the alignment of the road (slightly), and the fountain remains in the original location.

The second case study subject was the Athena Tacha in Cleveland, Ohio (c. 1985). The stepped granite fountain was designed to be ½ wet and ½ dry (the latter for students to perch upon). After running for eight years, the fountain was shut off due to issues with water leaks. A condition assessment found that the adhesive sealant, used to control water, had failed and resulted in water leaking to the dry side. Mineral deposits were also found on the stone’s surface, other conditions included broken pipes, corrosion, and inadequately sized equipment. The client also shared photos taken during the installation process, and Podnar noticed that it was the middle of winter. Low temperatures had also caused poor bonding of the stone to the continuous mortar bed. A full re-installation and equipment upgrade was recommended and subsequently executed. Stones were removed and labeled, and when re-installed provisions were made for water seepage to flow to the pool (at the base) and stainless steel clips were added to reinforce connections. Custom-fit pieces of sheet metal were installed to separate the wet and dry sides. The mechanical system was fully replaced (upgraded) and the access grate was designed to match the existing (granite) in galvanized metal, rather than stone, to facilitate maintenance with a lighter unit.

Voyage of Ulysses on Sixth Street in Philadelphia (c. 1977) was the subject of the final case study. The stainless steel fountain was fabricated by Lippincott and designed by David von Schlegell. During the condition assessment, Podnar found that the clear coating (applied to the metal’s surface) is failing and that the water display has been diminished (when compared with historic photographs). The fountain installation is located over a parking garage, and is leaking into it. The mechanical system consists of separated pumps for the two different display elements (high water throw on one side and a continuous waterfall on the other). Other findings include that the screen strainer has never been removed during maintenance and that over the years pumps were replaced with smaller ones. Podnar shared historic photographs taken during fabrication of the artist testing the water flow at Lippincott, emphasizing the importance of water flow in this fountain’s design. Conservation treatments are planned and have not yet been executed.

39th Annual Meeting – Research and Technical Studies Morning Session, June 2, “Acoustic Emission for Tracing Damage Directly in Works of Art” by Lukasz Bratasz

Acoustic emission measurements use microphones, amplifiers, and computers to detect and record the release of elastic waves during stress relaxation processes within materials, such as crack propagation at both the macro and micro scales. This talk discussed how acoustic emission (AE) has been used to track these processes in wooden and stone objects under varying levels of relative humidity and outlined how such studies have been used to generate and validate RH guidelines.

During AE experiments, the microphones are positioned against objects mechanically, without the need for glues or clamps, and environmental noise can be determined when there is sufficient distance between two sensors. It is important to note that recording AE monitors internal stress-relieving processes in real-time but is not able to predict when damage may occur.

The AE from wooden cylinders was found to depend on both the change in RH and the rate at which this change occurred. Mild changes in RH applied over 48 hours, for example, did not lead to detectable acoustic emissions. Monitoring the AE of a wooden altarpiece in a church lead to the establishment of expanded RH guidelines of 35 – 60% RH.

AE studies have also been performed on clay-containing sandstones similar to those found in medieval cathedrals. The studies monitored the sandstone’s response to damaging wetting-drying cycles and detected a linear AE increase with the number of cycles. The results of this study, in conjunction with predicted climate data, were used to anticipate areas of Europe in which clay-containing sandstones may be at particular risk for damage.

39th Annual Meeting – Research and Technical Studies Morning Session, June 2, “Listening to Art: An Exploration of the Use of Photoacoustic Infrared Spectroscopy in the Forensic Analysis of Artists’ Pigments” by Ian Butler

Dr. Butler described in this talk the potential use of Fourier transform photoacoustic infrared spectroscopy (FTIR-PAS) to identify organic and inorganic pigments. In their commercially available device, the sample is placed in a gas filled cavity and exposed to periodic flashes of infrared light. The sample absorbs the radiation and heats up, causing the surrounding gas to expand. The expansions can be detected as sound waves by a microphone at the end of the cavity.

The technique has been used to obtain reproducible IR spectra of pure pigments in the range of 400 to 4000 cm^-1 with a resolution of 8 cm^-1. Samples from lab-prepared frescoes have also been analyzed. In some cases the background noise from the plaster overwhelmed the pigment spectra, but in others the spectra could be used for pigment identification. Dr. Butler mentioned the possibility for depth-profiling, which may allow for more complex samples to be analyzed. Such work has not yet been carried out.

This method can also add some useful peaks to a regular FTIR spectrum, making it another useful option in conservation science’s identification tool-kit. Only small samples are needed and minimal preparation is required, an advantage over the commonly used ATR (Attenuated Total Reflectance) technique that may call for the sample to be crushed.

39th Annual Meeting – Research and Technical Studies Morning Session, June 2, “Medical Computed X-Ray Tomography and Volumetric Reconstruction for the Technical Examination of Organic/Composite and Ceramic Objects” by JP Brown

This talk presented case studies to demonstrate the application of computed tomography (CT) scanning to archeological objects. According to Dr. Brown, CT is usually available in most hospitals and can often be used for free in the evening. JP recommended first taking a regular x-ray of the object to elucidate its general construction. He did not go into details about the technical aspects of CT and image processing; however, this topic was covered by Hai-Yen Nguyen’s talk earlier in the session (An Open-Source Workflow for the Visualization of CT Data in Art Conservation and Archaeology).

Resolutions of 0.3-1.0 mm can be obtained by CT. The results are presented in Hounsfield units (HU), a scaled measure of the attenuation of radiation due to the material. Water is defined to have 0 HU, while air is defined to have -1000 HU. Typical HU values for metal and bone are 3000 HU and 1000 HU, respectively. Many image-processing techniques, such as the application of false-color, rely on the different HU values of different materials.

Case 1: Animal mummy

The CT images clearly showed that a piece had been inserted into the mummy, probably to hold the head at a desired angle. The detail obtained of the skeleton allowed for the species to be identified as a type of gazelle common in Egypt.

Case 2: Polychrome Japanese sculpture

The CT showed the grain of the wooden object in great detail, enough that non-invasive dendrochronolgy could be possible. This piece demonstrated the problem of having highly attenuating materials in the object – the bright images caused by leaded glass eyes obscured some of the nearby details. However, false-color rendering was able to show areas of gesso and older conservation treatments on other areas of the sculpture.

Case 3: Moche pottery

One of the aims of this study was to check for the presence of organic residues inside the vessels. This was done by comparing the HU values of the pots to those obtained from samples of various modern food residues. Although the CT of one of the pots did not indicate that food residues were present, the image showed a pattern of holes suggesting that the vessel was designed to produce sound from blowing air. A second pot was simply a conch shell, and the CT confirmed the expected internal structure. Interestingly, material inside a third pot did indeed exhibit attenuation values matching those of the test food samples. The material was subsequently collected on a swab, and SEM images indicated that the organic material was likely charred plant stems.

Case 4: Restored archeological stucco (possibly Sasanian)

The sculpture depicted the head of a king. The crown portion of the object, the shape of which could be used to identify the specific king, had been largely restored. Although it was possible to visualize only the original material by manual segmentation of the restored portions, not enough of the original remained for the identity of the king to be determined.

Several interesting points were raised during the question portion of the talk. It is known that x-rays affect the results of thermoluminescence (TL) dating, though it is not known to what extent. As a precaution, JP recommends removing a sample before CT scanning if TL may be performed later. Another interesting question regarded recommendations for approaching a hospital. JP suggested contacting the chief radiologist first, or ideally, finding a teaching hospital with a research radiologist. He mentioned that eventually an administrative/financial person will also need to be contacted and that having an exciting story about your proposed work will increase the chances that the hospital allows use of their CT machines.

39th Annual Meeting – Research and Technical Studies Morning Session, June 2, “An Open-Source Workflow for the Visualization of CT Data in Art Conservation and Archaeology” by Hai-Yen Nguyen

This talk discussed how open-source image-processing software can be used to manipulate data obtained from computed tomography (CT) scans of objects. In this technique, radiographs are taken around an axis of rotation, and the three-dimensional volume of the object is virtually reconstructed. From JP Brown’s talk (Medical Computed X-Ray Tomography and Volumetric Reconstruction for the Technical Examination of Organic/Composite and Ceramic Objects), we learned that it is relatively easy to gain free access to CT equipment at local hospitals. However, as Hai-Yen pointed out, the proprietary software for processing the data can cost around $15,000. By using several open-source programs, she and her co-workers were able to obtain quality images highlighting various aspects of the object under study.

CT images of a corroded metal artifact in a tub of water were presented at various stages of processing with different software programs. A median filter was applied in ImageJ to reduce noise. Most other processing applications were performed in ImageVis3D, including thresholding, slice analysis, and manual segmentation. The 16-bit raw tiff file formal was considered the most user-friendly for transfer between the software systems.

After the initial data processing, Hai-Yen demonstrated the use of false color to clearly show different types of material and used clipping (masking) to isolate certain features. Once a complete 3D rendering is obtained, it could potentially be used to create a physical model of the artifact without the need to dry out and clean the original.

Disclaimer: Neither of us bloggers has ever done CT or this type of image processing, so we may have missed salient details. Feel free to add information in the comment section below.

39th Annual Meeting – Research and Technical Studies Morning Session, June 2, “Silver Nanoparticle Films as Sensors to Measure the Emission of Sulfur Gases from Wool Fabrics Degrading Under Ambient Conditions” by Rui Chen

Dr. Rui Chen has been developing optical sensors using silver nanoparticles for the detection and quantization of sulfurous gases. These sensors are meant to serve as an improvement over the metal coupons used in the Oddy test, as silver nanoparticles react faster and with higher sensitivity than bulk silver. Additionally, their reaction with hydrogen sulfide causes the nanoparticles to lose their color, so the kinetics of the reaction can be monitored spectrophotometrically with the decrease in the absorbance spectrum.

To make the sensors, spherical yellow nanoparticles are assembled as a monolayer on a glass surface with a polyethylenimine linker. When the monolayer films are exposed to hydrogen sulfide gas, the observed decrease in absorbance is faster when the concentration of hydrogen sulfide is higher. At concentrations of 10 ppm hydrogen sulfide, for example, the reaction is complete within about an hour, while completion occurs within 4 to 6 minutes at concentrations of 100 ppm.

Furthermore, Dr. Chen has found a linear relationship between the first-order rate constant for the reaction and the concentration of the gas. Thus, an unknown concentration of hydrogen sulfide gas can be calculated based on the reaction rate observed between the gas and the nanoparticle-based sensor.

The sensors have been applied to wool samples aged under UVB light. These samples exhibited the highest emissions within the first 400 hours of aging, with concentrations of hydrogen sulfide reaching nearly 600 ppb per gram of wool. The sensors have also been applied to photograph cases and a box containing naturally aged silk fibers; four of the five objects tested exhibited some emission of hydrogen sulfide to give concentrations that ranged from 33 ppb to about 150 ppb. Future work on this project will involve the development of a user-friendly protocol for the application of the sensors.

39th Annual Meeting – Research and Technical Studies Morning Session, June 2, “Measuring Changes in the Appearance of Surface Textures” by Paul Whitmore

The ability of conservators to accurately describe surfaces is integral to effective documentation and communication in the conservation field. While changes in color can be accurately described by the Munsell and CIELAB systems, changes in the appearance of a surface texture are often described by vague and indefinite terms. The work described by Dr. Whitmore arose from the desire for a new vocabulary for describing the surface texture and appearance of regularly-patterned surfaces such as canvas. His talk presented a background of how we perceive surface texture and some mathematical analyses that can be performed to yield qualitative metrics for describing certain textures.

Texture is not only an artifact of the topography of a surface, but also a result of the illumination of this topography; the appearance of a surface depends on the position and directionality of the light source as well as the distance of the light from the surface. As viewers, we perceive texture from the resulting distribution and contrast of light and dark areas.

The limitations of our perception can be mapped by a contrast sensitivity function, which relates our ability to perceive patterns of varying degrees of contrast with the size of the pattern and the distance at which it is viewed. Changes to texture are often accompanied by changes in contrast; a weathered surface, for example, exhibits decreased contrast between its light and dark areas. In periodic patterns, the contrast can be quantitatively measured by a gray-level correlation matrix analysis. Once this contrast value has been determined, the contrast sensitivity function can be used to calculate the maximum viewing distance at which a pattern of the given contrast can be perceived. This “maximum visibility distance” may serve as a useful metric with which to describe periodic surface textures.

The analysis has been successfully applied to canvases that had been subjected to extreme treatment, and further work will examine the degree of textural changes caused by common conservation treatments. Future work may also investigate other mathematical and image processing analyses for application to different surface textures.

AIC’s 39th Annual Meeting – Paintings Morning Session on June 3, “Industrial Literature as a Resource in Modern Materials Conservation” by Dawn V. Rogala

Artists working in the post-WWI era frequently used industrial products in their work. This can put conservators in the position of dealing with materials with unknown compositions and behaviors that are not conducive to long-term preservation. Unfortunately, existing conservation literature does not always provide adequate materials information or case studies for conservators wrestling with these issues. Expanding literature searches to include period industrial articles can fill in those informational gaps.

Dawn Rogala discovered the benefits of such industrial literature while researching mid-century American oil-based zinc oxide house paint during her postgraduate fellowship at the Smithsonian Institution in Washington, DC. Her research focused on a group of abstract expressionist paintings and the relationship between their zinc oxide grounds and failure of the paint layers. She found that industrial literature provided significant evidence of a connection between the choice of materials and the current unstable condition of the paintings.

The period between 1925 to 1950 provided Rogala with the most useful articles, likely due to market demand and frequent product adaptation during that time. The largest percentage of articles she found were presented by representatives of the paint manufacturers who were focused on promoting the benefits of their paint to consumers. Those may seem like biased and unreliable sources for accurate information, however such articles often mentioned engineered mechanical behaviors that were considered beneficial in their paint films. Approximately 25% of the articles in her research were affiliated with scholarly research. Those articles provided more comprehensive and practical analyses of paint film behaviors with useful reference bibliographies.

Weathering test articles were another rich source of information on paint formulations and behaviors. The variations in regional weather often caused adaptations in regional paint formulations. This meant that artists working with a zinc oxide house paint in a mild climate may have worked with an entirely different formulation of zinc oxide house paint than an artist working in a more severe climate during the same period. It also suggested titanium dioxide’s introduction into house paints in the mid-1950s could have been delayed on a global scale when considering issues of climate influences on formulation changes.

One of the specific examples Rogala gave to illustrate the usefulness of industrial literature referred to self-renewing paint films. Weathering test articles cited a preference for acicular particles because their brittle nature allowed for microfissures in the paint, which would cause it to slough off in the rain and result in a crisp clean surface. Another example was the mention that three years was the required life expectancy for engineered paint films according to industrial standards. While such qualities were acceptable and even desirable in house paints, such paint films pose clear disadvantages for conservation. In fact, Rogala pointed out a 1909 article that warned about the dangers of zinc oxide paint as a ground layer!

I thought this was an outstanding presentation. Conservators must be resourceful and adaptable when dealing with unknown, unpredictable materials. This is a particular necessity when it comes to the conservation and preservation of modern and contemporary artwork. I appreciate Rogala’s study for delving into the industrial side of zinc oxide and providing an open look at a somewhat unconventional resource for conservation research.

39th Annual Meeting – Joint Paintings/Research and Technical Studies Session, June 3, “Speed, Precision, And A Lighter Load: Metigo MAP 3.0, A Great Advancement In Condition Mapping For Large-Scale Projects” by Emily MacDonald-Korth

Emily MacDonald presented on the usefulness of a new condition mapping program called Metigo MAP 3.0. She began her presentation with a description of a collaborative project between the University of Delaware and the Tsinghua University (Beijing) led by Dr. Susan Buck (Winterthur/University of Delaware Program in Art Conservation) and Dr. Liu Chang (Tsinghua University) to examine and document Buddhist murals and polychromy in the Fengguo Temple (Fengguosi), located in Yixian County, Liaoning Province, China. The four interior walls of the temple are lined with the murals. The murals were in very poor condition and their contained images were skewed by loss and other damage.

The Metigo Map software allowed the conservation team to map the murals’ condition issues in a short period of time. The software incorporates mapping, digital imaging, and area measurement tools. The program streamlines the mapping process and is easy to use. Emily compared the software to known and used techniques of documentation and illustrated the limitations of each.

Metigo Map was created by German company fokus GmbH Leipzig, dedicated to architectural surveying in addition to documentation of large scale conservation projects.

Maps are produced by uploading images into the software. The images can then be drawn on and annotated. The program makes the image true to scale and is able to rectify skewed images to proper orientation. This allows images to be used that were taken from an angle if your subject is not accessible from the front. By inputting the dimensions of the painting, the software can give exact locations of areas of interest and calculate the surface area of damage. This feature can also be useful in making time estimates for proposals on big projects. Image processing setting allows for photo editing to aid mapping. Mapped images can then be exported as tif. files and opened in other programs.

For the presentation, Emily chose three murals to be representative of the condition issues they noted overall. The conservators worked as a team, using Metigo Map to document the condition of the murals. After the murals are mapped, the maps can be compared easily for condition issues. The software can also be used to map the locations of samples. Annotations can be made to the maps for future referral.

For large scale projects or projects particularly difficult to photograph, users can use the tiling function of the software to piece together the rectified image. This allows for seeing the project unobstructed.

Emily also illustrated how Metigo map can be used to document experiments. She has also used the software while working on a graffitti removal research project at the Getty to document surface changes and areas of treated surfaces.

Emily summed up the talk with an excellent slide comparing the pros and cons of the software. The pros included: easy mapping, image processing, rectification, measurement functions, compatibility with other software, and easy interface. Cons included: requires initial training, no white balance (but this can be done on photoshop beforehand), and cost (more expensive than adobe creative but less expensive than autocad).

39th Annual Meeting – Joint Paintings/Research and Technical Studies Session, June 3, “Raman Revealed: A Shared Internet Resource for the Cultural Heritage Community” by Suzanne Quillen Lomax

Suzanne Lomax presented on IRUG’s (Infrared and Raman Users Group) latest efforts to distribute data for Raman spectra. She began the talk with a brief discussion on the history and mission of IRUG and their new initiative to create a Raman spectra database due in large part to a $239,650 two-year IMLS grant awarded to the Philadelphia Museum of Art in partnership with IRUG. The 118 institutional members will contribute to the database which will be used by individuals, scientists, conservators, and students to study cultural heritage. The Raman database will be maintained on their website. IRUG has biennial conferences and their website www.irug.org contains information on grant funding and the conferences. All of the coauthors for this paper are board members of IRUG.

Suzanne described the model for the database and compared it to the widely used infrared database. By 2009, the IR database was 100% digitalized, available on CD, and in two print volumes. The latest edition contains over 2,000 infrared spectra. On the current IRUG website, members are able to search terms and match by keyword resulting in a hit list for searched components. The resulting spectra provide in their file name link the mode of collection and where it was collected. The largest represented group in the IR database is organic dyes and pigments followed by mineral pigments. Raman spectra are currently being collected and added to the database.

Suzanne also stressed the growing use of IR and Raman data use in the field and how this is being reflected in papers at IRUG conferences specifically related to art and archaeology. She provided examples in which mineral pigments as well as synthetic organic pigments have been identified though used of the database and how Surface enhanced Raman spectroscopy (SERS) can be used to overcome the problems of fluorescence by using nanoparticles to magnify the signal.

Objectives of the IRUG database will include a website interface with the ability to upload data by users, software, a translator to transform native data into IRUG standard, a searchable library, an interface for keyword searches, data download, and spectra printing.

Suzanne is chair of the newly formed Raman review committee, which reviews spectra and format. The format to be used by IRUG is JCAMP-DX (ASCII) files for universal access. This will also allow batching of spectra for submission. To learn more about the format refer to the IRUG website.

The first batch of spectra has been pledged but the invitation is open to new contributors. Interested people should contact Suzanne or Beth Price, the project manager from the PMA. Currently users cannot upload data but can do searches on the website.

A comment after the talk reminded the audience that it is a free database though users need to contribute 10 spectra to get access to the searchable version.