AIC’s Annual Meeting – Page 33 – AIC Blog Archives: Conservators Converse

42nd Annual Meeting- OSG + RATS Session, May 30, “Blue, Red, and Wound All Over: Evaluating Condition Changes and Cleaning of Glass Disease on Beads” by Robin O’Hern and Kelly McHugh

Glass disease, weeping glass, glass deterioration, funky glass* (*author’s description)–just a few of the many names used to describe the degradation of glass beads that museums have observed as a white precipitate/cloudy appearance and/or cracking and splitting. If you’ve observed this in your collection, take notice- Mellon Fellow in Objects Conservation, Robin O’Hern, is on the case.
O’Hern has taken advantage of the history of glass disease detection at the National Museum of the American Indian (NMAI) and begun evaluating how the different cleaning methods have fared over the years. In 1999, Kelly McHugh (research supervisor and co-author) and Scott Carrlee performed a condition survey of the NMAI collection. The collection was moved into a state-of-the-art storage facility after the survey, where the RH has remained constant, but at a higher level than recommended for glass pieces. (The beads are present on composite pieces with hide, bone, shell, feather, hair, etc. and therefore the environmental controls must address as many materials as possible, not just glass.) Some of the pieces were treated at that time, and others have been treated in the interim years. Using the museum database, O’Hern found that 25% of the condition records that list glass beads as a material also list glass disease. O’Hern has performed another survey, this time seeking to observe condition changes over the past 15 years in a selection of objects from the 1999 survey, to assess treatment technique (ie, which solvents worked best to reduce glass disease), and to discover susceptibility trends (which beads are the worst culprits).
To understand the beads, O’Hern provided background on history of use and manufacture.

Glass beads arrived after contact with Europeans in 1492
Pony beads were introduced after 1675
Wound beads were introduced after the late 17th century
Seed beads were introduced 1710-1840
Red beads were colored from copper in the 17th century, ruby red in the early 18th century, and selenium in the 1890’s
Blue beads were colored from copper or cobalt, but from 1640-1700, they were tin-rich
Beads can be made by pulling the heated glass, called “drawn,” or by winding heated glass around a rod, called “wound”
Glass is made from silica, alkali (to lower the melting point, but also makes it water soluble), and calcium carbonate (that turns to lime- it’s added to help stabilize the glass after the alkali)

There are several explanations for the cause of glass disease. Too little or too much of the lime (part of the bead’s composition) may cause water to leach out of the glass matrix as ions that then form salt on the surface of the bead. The environmental conditions, such as fluctuations in RH, or materials in proximity, such as semi-tanned hide, may accelerate glass disease. As seen from the list above, the beads were manufactured over a range of time, in different ways, and in different places.
As you can tell, there are many factors to research when evaluating glass disease. O’Hern addressed as many as possible while still managing the scope of the project.
Survey Results
Condition Change: By comparing condition of the beads today to past condition/treatment reports, 16% of the beads have more deterioration now than in 1999. Measuring pH was used in addition to visual examination to determine condition. Some beads that did not look bad had a higher pH (above 7), signaling glass disease. Some beads that looked hazy did not have a higher pH, meaning no glass disease (perhaps hazy from manufacture).
Differing Manufacturing Techniques: Wound beads have it worse than drawn beads–95% of wound beads have glass disease. This could be because they have a compositional percentage of lime that is less stable.
Differing Colors: Black, red, and blue are the most disease-ridden. O’Hern looked through the museum database and found that the entries with the most “glass disease” indicated had blue beads. Blue beads are very clearly the “winner” of the glass disease competition, followed by red and black.
Treatment Techniques: Here’s where it gets even more interesting. The conservation literature and posts on the Objects Specialty Group list serve debate the use of three solvents to remove the salts on glass disease: water alone, ethanol alone, and a 1:1 water:ethanol mix. By comparing the 1999 survey to her own results, O’Hern capitalized on real-time aging to observe how each solvent mixture fares over time. Water-cleaned beads had a 50% rate of glass disease return; water:ethanol-cleaned had a slightly higher than 50% rate of return; ethanol-cleaned had the least amount of return at just under 50%. However, when looking at the beads cleaned with ethanol over the same time period as those cleaned with 1:1 water:ethanol (removing the very oldest treatments), the rate of return for glass disease falls to 40%.
(Note: Acetone has also been listed as a solvent for cleaning glass beads, but since the NMAI doesn’t use acetone, it was not included in this research.)
Other Observations:
1. Measuring pH is essential because beads may look like they don’t have glass disease, but are actually more alkaline. Measuring pH is also quick and easy- cut your pH strip to a small piece, slightly dampen it in deionized water, press it onto the bead for 3 seconds, and then determine any color change in the strip.
2. The most affected beads were those sewn onto hide, but the disease was present when beads were in contact with many other materials as well.
3. Although cleaning with ethanol is a better choice for long-term disease prevention, the solvent chosen should still depend on the substrate around the bead.
Advice from O’Hern:
1. Record treatment materials when removing glass disease.
2. Take BT and AT details of beads so you can easily compare for condition changes in the future.
3. Measure the pH of the beads… and RECORD THE RESULTS.
4. Have consistent monitoring of glass disease.
As an audience member, it’s always exciting to see a project that has results, especially on a topic that is not studied as extensively as it persists. This is definitely a postprint worth visiting for more details and results.
For other examples (and some “good” photographic examples), visit Ellen Carrlee’s project “What’s that White Stuff?” that she and (then WUDPAC graduate intern) Christa Pack reported on in Ellen’s blog: http://alaskawhitestuffid.wordpress.com/2011/08/09/glass/

42nd Annual Meeting – Joint PSG/WAG Session, May 31, 2014, “Recent Developments in the Evolution of Spring-loaded Secondary Supports for Previously Thinned Panel Paintings”, by Alan Miller and George Bisacca

In his presentation, Alan Miller, Assistant Conservator in Paintings Conservation at the Metropolitan Museum of Art in New York, showcased recent developments of spring-loaded secondary supports attached to the back of panel paintings.
He began by reviewing how usual 19^th and 20^th century treatment of warped panel paintings involved severe thinning of panels along with the application of wood “cradles” on their backs to straighten them and provide “support”. This portion of the presentation wonderfully complimented Karen French’s earlier talk on the evolution of the structural treatment of panel paintings at the Walters.
As Karen did in the morning, Alan discussed the consequences of past treatments on the panel and its painted surface. New treatment approaches have evolved over the past two decades with the development of flexible supports attached to the back of panels, allowing for the natural curvature of the wood and its movement in response to changes in relative humidity. Specific consideration was given to previously thinned panels, very vulnerable once their cradle is removed. Alan provided a review of the development of the spring mechanisms they developed with George Bisacca these past years, referring to the Getty Conservation Institute’s panel paintings initiative (link: http://getty.edu/conservation/our_projects/education/panelpaintings/panelpaintings_component1.html)
The presentation was generously illustrated with images of the various spring mechanisms developed at both the Istituto Superiore per la Conservazione ed il Restauro (ISCR) and later by Bisacca and Miller, explaining the pros and cons of each. For instance, the earlier conical spring designed at the Istituto allowed for much movement but required thickness of the wooden strainer attached to the back of the panel painting, an issue in terms of flexibility of the strainer, not to mention weight and volume. On the Met’s most recent strainers, which are much thinner, grooves are cut cross grain and filled with a silicon based material for added flexibility. Miller emphasized the importance of the number and placement of the springs attached to the back of a previously thinned panel.
He listed the criteria established for the development of spring mechanisms specifically designed for previously thinned panels: springs should be as small (contained) as possible to allow for a thin strainer, easy to adjust, economical and re-usable. Most recently their work has focused on a thin laser cut disk spring, associated with a flexible threaded nylon screw, which allows light weight, flexibility and fine adjustment.
This talk provided very valuable information on recent developments in the treatment approach of wooden panels, applicable not only to paintings but possibly to furniture or architectural wooden panels.

42nd Annual Meeting – Wooden Artifacts Group Session, May 29, 2014, “Review and interpretation of X-Rays of construction details of American seating Furniture”, by Gordon Hanlon

In his talk, Gordon Hanlon discussed a project that started at the Museum of Art Boston (MFA) in 2005 around a controversy regarding the date of manufacture of a side chair by Philadelphia furniture maker and carver Benjamin Randolph (1721-1791). In his 1972 book American Chairs, Queen Anne and Chippendale, John Kirk argued that a chair bearing a Randolph label and its mate – both in the Karolik Collection at the Museum of Fine Arts, Boston – were out of period. Consequently, both objects were removed from exhibition. Kirk’s analysis was refuted twenty six years later by Philip Zimmerman in an article published in American Furniture, entitled “Labeled Randolph Chairs Rediscovered”, available online at: http://www.chipstone.org/html/publications/1998AF/Zim/1998ZimIndex.html. While the Museum of Fine Arts was preparing for the opening of its new American wing, the Randolph chair was X-rayed to study its joinery. This examination confirmed Philip Zimmerman’s judgment that the chair’s construction was consistent with period manufacture techniques, most likely around 1765-75. This investigation was the start of a much larger campaign of study of chairs’ construction through X-Ray examination.
The MFA collection counts 278 American chairs, from early 17th c. to 1950, allowing for thorough comparison of construction techniques and tool marks associated with joinery. The Furniture laboratory started x-raying chairs as they came into the lab, which worked well in conjunction with the American wing project. One type of chairs did not lend itself well to that type of analysis: painted seats with lead based ground.
When film was used in the initial phase of this project, it was scanned at 300 dpi. The file was then enhanced in photoshop, using for instance the “unsharp mask” tool, then brightness and contrast adjustments. Many other options are of course available to reveal various levels of information on the image. The MFA recently switched to digital X-Ray, which seems to surpass film from Gordon’s point of view.
In order to compare information revealed by the X-Ray images, Gordon made mock-ups of joints and looked at a selection of bits. 36 chairs have been x-rayed so far. A few examples were illustrated in the talk, showing tenon and mortise joints as well as dowels.
To record the data gathered, TMS database showed some limitations, leading the lab to use Filemaker pro. The lab already had experience with this database as they used it for two previous projects: in 2005 for a study of historic fasteners (Chris White), and in 2008 for an investigation of painted furniture (Carola Schuller and Michelle Derrick). Currently Christine Schaette, who also gave a talk during this WAG session, is also using Filemaker pro to record her findings on inscriptions found on furniture. Gordon concluded his talk by inviting his colleagues to share results of their own examination of seats. This is something to investigate for WAG, to hopefully find a way to create a platform for everyone to share X-Rays of chairs.

42nd Annual Meeting – Photographic Materials, May 31, "Retouch Practices Revealed in the Thomas Walther Collection Project" by Lee Ann Daffner

MoMA‘s Thomas Walther collection contains over 340 photographs Walther collected from 1909 to 1949 in Eastern Europe, the United States, and Paris. Many of these photographs will be on exhibition at MoMA between November 08, 2014–April 26, 2015. The departments of Photography and Conservation at MoMA have been collaborating on researching this collection of Modernist photography which will culminate with a publication that will be available in early 2015 and a symposium on December 12, 2014. The results of this collaborative research will also be available on the OBJECT:PHOTO website which will include a timeline of Walther’s life and identification of photographs by location. The research Lee Ann presented at AIC focuses on artists’ working methods, specifically retouching techniques. Retouching can be done to either a print or a negative to enhance effects or mask imperfections. Retouching includes reductive techniques (such as scraping) versus additive techniques (painting, drawing, etc.), and an artist’s discretion to use any of these techniques can inform the viewer about the photographer’s intentions.

Summary by Greta Glaser, Owner of Photographs Conservation of DC

42nd Annual Meeting – Photographic Materials, May 30, "Preservation of Deborah Luster's One Big Self" by Theresa Andrews

Luster is a Louisiana based artist who began her own career in photography in 1988 after the death of her mother. Both her mother and grandmother were photographers. One Big Self is an artwork comprising 287 4″ x 5″ silver gelatin developed out photographs on aluminum plates, stored in a steel cabinet with three drawers, and a lamp on top of the cabinet to facilitate viewing. The photographs are portraits of Louisiana prison inmates taken between 1998 and 2002. On the back of each metal plate is a personal description of the person in each photograph. The artwork is intended to be interactive, allowing the viewer to handle the photographs and read the inscriptions, seeing the subjects as real people. The metal plates are covered in paint, followed by the gelatin emulsion layer used to print the photographic image which is selenium toned. Creating these plates is very labor intensive, and Luster only manages to produce three to four plates per day. She inscribes the personal information about the inmates on the plates with a dremel tool.
The San Francisco Museum of Modern Art (SFMoMA) was faced with the challenging task of displaying One Big Self in the way the artist intended – as an interactive work – after it was acquired in 2003. The security and physical preservation of the photographs were the two biggest threats to the work. The piece ended up being displayed alone in a room with one museum guard on duty at all times, which seemed appropriate in the context of the artwork’s subject matter. It was decided that only 200 plates would be displayed at any time, and twenty portraits were randomly selected to never be displayed. The plates that have been on display have indeed seen changes. Some plates have been caught in the drawers and become bent, edges of the emulsion on some plates have been abraded, and some of the plates have yellowed. Although the artist is dismayed at learning about the yellowing, the cost and time of replacing each plate as it becomes too worn to be viewed makes reprinting each portrait an inefficient solution. Out of the total 287 plates, excepting the 20 that will never be displayed, only 200 are on display at any given time, so 67 plates can still be swapped with any plates that become too damaged for exhibition.

Summary by Greta Glaser, Owner of Photographs Conservation of DC

42nd Annual Meeting – Photographic Materials, May 30, "Fototeca Pedro Guerra: Conservation of the Photographic Archives" by Cinthya Cruz

The archives of Pedro Guerra are part of the Universidad Autónoma de Yucatán in Mérida, where the climate is hot and humid. Photographic prints and negatives in this collection include many photographic processes and materials, from albumen and silver gelatin to glass plates and nitrate negatives. The goals of the photo archives are to stabilize the existing materials, catalog and organize the objects, and monitor and maintain a safe environment. Condition issues affecting the collection include broken and scratched glass, finger prints, sticky emulsion, and fungus. Nitrate negatives are immediately placed in frozen storage in Marvelseal bags after they are treated and scanned. Object codes and registration numbers specific to the archive are written on the exteriors of the bags so negatives can be located when necessary. Enclosures for other photographic materials, such as sink mats for broken plates and acid-free paper envelopes for photographic prints, also contain object codes and registration numbers. The object codes refer to the subject matter contained in the photographic image and the type of object.

Summary by Greta Glaser, Owner of Photographs Conservation of DC

42nd Annual Meeting — Book and Paper Session, May 30, "The Conservation of Tiffany Studio Drawings: Finding New Ways to Reconstruct Complex Paper Loss," by Marina Ruiz Molina

Two of the motifs in the book and paper presentations and posters this year were 1) paper pulp, for example in Debra Evans and Victoria Binder’s poster “Pulp Addiction: The Use of Dry Cast Pulp,” and Renate Mesmer and Jennifer Evers’ poster “Cast Paper Pulp,” and 2) flood and mold damage, which were represented in Katherine Kelly and Anna Friedman’s presentation “Conserving the Iraqi Jewish Archive for Digitization” and Fernanda Mokdessi Auada’s “Salvage of Paper Materials from the Flooding of Saõ Luiz do Paraitinga.” Marina Ruiz Molina’s presentation united these themes, in using paper pulp to conserve mold damaged items.
Marina Ruiz Molina’s case study objects were part of a collection of drawings used as guides in the Louis Comfort Tiffany studio in manufacturing stained glass. The firm went out of business in 1924, and the drawings were later found in an attic room of a marble dealer in Long Island. The collection entered the Metropolitan Museum of Art in the 1960s but they have been inaccessible due to their extensive mold damage from water damage, as seen in this combined before and after treatment picture.

Before (top) and After (bottom) of mold-damaged Tiffany drawing — Before (top) and after (bottom) pulp infill and overlay of mold-damaged Tiffany studio drawing

Marina Ruiz Molina gave a quick overview of mold and what it does to paper, causing both structural weakening and aesthetic damage from the pigments it produces. She then presented three case studies of the use of cast paper pulp. The Tiffany drawings had been executed on illustration board that was made of imported Whatman paper adhered to local wood-pulp board. She first mechanically reduced the mold by cleaning with suction under the microscope, followed by application of solvents, enzymes and chelating agents in an attempt to reduce the stain.
The paper was still stained and extremely weak. The weakness of the original paper made it especially important to match the strength and expansion properties of the infill to the original paper. Marina Ruiz Molina achieved this by mixing cotton and flax to get the right hydrophilicity and using pre-dyed reactive dye pulp to achieve the right color. She is still experimenting with pigments, but the dyes were much easier to work with. She beats the pulp with a Vita-pro3 Vitamix blender, using the blending time to control the properties. She has found that any blend time under about 30 minutes still gives good fiber length.
Once the pulp is prepared, she pours it onto a Hollytex screen (the 0.0029” Hollytex is an ideal weight). She taps the fibers with a brush to distribute the fibers and then lifts the whole screen onto blotters. For the first case study, she cast two sheets, one as an infill and one as an overlay. To adhere them she humidified the object along with the infill and sprayed the infill with a dilute methyl cellulose solution, aligning it over the drawing on the suction table.
In the second case study, the decision was made to leave the drawing on its illustration board and to mechanically remove only the damaged part of the board, cutting it away in a stepped pattern to give a better surface for infilling. Marina Ruiz Molina then adhered several layers of Richard de Bas paper to build up the inner layers, using methyl cellulose. The outer visible layers were cast paper fills.
The third case study had thin lines on the recto traveling into the mold damaged area. Marina Ruiz Molina showed pictures of casting the overlay with holes in it so the design is still visible.
Marina Ruiz Molina is still refining the technique and would like to compare dyed pulps and pigmented pulps with a microfadeometer, investigate the quantitative effects of different blending and drying techniques, and find more sustainable methods for cast paper fills.

42nd Annual Meeting – Conservators in Private Practice, May 28, "Greening your Conservation Practice."

“Believing heat wheels work is like believing you can section off a part of a hot tub for peeing.”

Headline speaker Monona Rossol began this year’s CIPP workshop with her characteristic flair when referring to the use of the heat exchange system with contaminated air streams. The system is often recommended to score points for Leadership in Energy & Environmental Design (LEED) certification and served as an example of how greener practices may not necessarily be safer practices. An Industrial Hygienist and health and safety champion for the arts community, Monona is the founder of Arts, Crafts and Theater Safety (ACTS). If you don’t leave one of her lectures concerned about everything you have ever come in contact with, you should at the very least have a better idea of how to navigate your way through the jargon of government, industry and product health and safety information.
The beginning of Monona’s talk introduced the pitfalls of blindly accepting the safety information provided by government regulatory organizations and manufacturers. In her explanation of many of the acronyms associated with chemical classifications and exposure assessments, Monona emphasized that it’s what we don’t know about chemicals that is the most concerning. For example, phrases such as “not listed as a carcinogen” and “generally recognized as safe” do not indicate that the chemical is not toxic, but may mean that it has never been tested. She also reviewed the improved chemical labeling and Safety Data Sheets (SDSs), as outlined by the new OSHA Hazard Communication Standard. Even though SDSs are better than their predecessors, Material Safety Data Sheets (MSDSs), they still are limited by lack of information. Finally, she discussed commercially manipulated and undefined “green” phrases like all natural–just because something comes from nature does not make it is safe–and biodegradable– chemicals can breakdown into compounds that can be more toxic than what you started with.
So what can we do as conservators and consumers to protect ourselves, the others we work with and the environment?

Become a conscientious and informed user; understand and learn about the products in your studio as well as the language and limitations of hazard communication (such as manufacturer provided SDSs) and local and federal regulations.
Purchase products from companies that disclose the full ingredient lists and avoid products that have proprietary formulations.
Support laws such as California’s PROP 65, which requires the state to publish a list of toxic chemicals. Businesses must notify Californians about significant amounts of chemicals in their products or that are released into the environment. By allowing anyone “acting in the public interest” to enforce the law, it takes the responsibility for policing manufacturers and their harmful materials out of the hands of legislators and bureaucrats and into the hands of the people who are being affected by toxic chemicals (you!).

In the second half of her presentation, Monona discussed air quality and fume and particle extraction. She first reviewed the definitions of gases, vapors, fumes, dusts, mists, nano-particles and smokes; their associated health hazards; and types of filters that can be used. In her discussion of fume extraction, she cautioned that window fans and air conditioners are not proper ventilation and of the limited efficacy of portable, filter-based fume extractors. Her main point was that proper extraction involves a displacement system that exhausts to the exterior in concert with bringing in uncontaminated air from a source on a wall across from the exhaust (not from an adjacent wall or window). A clear path of air flow should put the conservator’s head directly in the stream. Filter-based extractors can be selective to the vapors and/or particles sizes they collect; only clear the immediate work area; do not provide clean replacement air; and have no indication of when the filter is no longer functioning properly. She stressed that when you are designing your ventilation system, you should consult a specialist with an industrial ventilation background. While there were too many points to discuss in a few hour workshop and certainly too many to adequately cover in a blog, Monona is always willing to respond to anyone’s concerns or review your studio set-up.

The remainder of the session focused on greener business practices. Chair of the Committee on Sustainability, Betsy Haude, outlined the committee’s activities over the past year, including several AIC News articles and making their wiki into an informative and useful resource.
Objects Conservator Sarah Nunberg, followed up with an outline of the results of a Life Cycle Assessment to look at the environmental impact of museum practices. Conducted in collaboration with the Boston Museum of Fine Arts, students at Northeastern University performed four case studies using a computer program with a series of user defined parameters: 1) halogen vs. LED lighting, 2) solvents used for consolidation of stone, 3) loans and transport, and 4) HVAC systems. They concluded that the LED lighting was more energy efficient. In the second case, silane in ethanol proved to have the greatest negative environmental impact over B72 in xylene and B72 in acetone and ethanol; xylene had a greater impact than acetone/ethanol primarily due to its production. In their loan assessment they compared a loan going to Tampa, Florida and a loan going to Japan. Interestingly, they discovered that accommodating for the courier had the greatest environmental impact. Finally, their study also showed that shutting down HVAC systems every night decreased the energy costs by 40%, but that the overall energy impact also depended on the source. Seeing quantified data on these various museum conditions allows for a discussion on how museums can potentially reduce their environmental impact, while still considering the elements of maintaining and promoting their collections.
The final three San Francisco-based speakers discussed the various programs that are available for greening business in California. Wendy Yeung of the California Green Development Program presented on how this government program works with local business to implement environmental protocols that are both sustainable and profitable. Anya Deepak, a Commercial Toxics Reduction Associate with the San Francisco Department of the Environment, discussed their program for artists, which is an outreach initiative to raise awareness among Bay Area artists on environmental and health issues associated with their art materials. The program is currently in the first phase of implementation and will eventually address disposal, safety and finding alternatives. Organizers discovered they were able to get remarkable participation and interest from all the studios they contacted by suggesting that the artists could have an effect on the environment by following these practices–a notably more positive response than when they tried to appeal to the artist’s personal health and safety. Finally, Anna Jaeger from Caravan Studios, a division of TechSoup Global, discussed various electronic and tech-based programs for greener business administration. Her examples focused on the idea that it is more effective to change the situation or environment than to change an individual’s behavior. Tips included using smart power strips and multi-function machines; conducting virtual meetings; and purchasing refurbished electronics since the majority of energy use goes into their production.
The seminar concluded with a group discussion of what sustainability means to us and the field of conservation. Can artifact preservation and environmental preservation coexist? How can we make the annual meeting more sustainable? Should ventilation regulations focus on optimal human performance within that space or optimal environmental impact?

42nd Annual Meeting – Photographic Materials Group, May 31, “Comparative Study of Handheld Reflectance Spectrophotometers” by Katie Sanderson

Katie Sanderson, Assistant Conservator of Photographs at the Metropolitan Museum of Art (MMA), presented a most informative comparative study of handheld spectrophotometers undertaken at MMA. When the Department of Photograph Conservation decided to replace its existing handheld spectrophotometer—an X-Rite 968—Sanderson along with Scott Geffert, Senior Imaging Systems Manager, researched current units available to determine the best replacement and variation in measurements taken by each.
Sanderson began by outlining the factors to consider when replacing a spectrophotometer: data continuity (extant data over 20 years); instrument agreement; data translation; software compatibility with previous and future instruments; and longevity and support (the previous spectrophotometer is no longer supported by X-Rite but still takes good data readings). In total, seven spectrophotometers—four by X-Rite and three by Konica Minolta—were tested against the MMA’s X-Rite 968 and a bench-top spectrophotometer equipped with an external remote diffuse reflectance accessory probe in the Department of Scientific Research. The seven spectrophotometers examined were:

X-Rite 964
X-Rite eXact
X-Rite Ci64
X-Rite RM200
Konica Minolta 2600D
Konica Minolta 2500c
Konica Minolta FD-7

Before delving into the specific finding of each unit tested, Sanderson provided a brief overview of how spectrophotometers work. She explained that an object is illuminated by a light source of a specific spectral range, a detector collects any reflected light, and a unique spectrum is produced. While some light sources extend into the ultraviolet region of the electromagnetic spectrum, most are within the range of visible light (400-700nm). The two most common geometries for spectrophotometers are 0/45—in which the first number represents the angle (in degrees) of the light source and the second number the angle of the detector—and integrated spherical.
As Sanderson described, some of the units tested had an integrated spherical geometry that takes into account specular reflectance; these spectrophotometers can be operated in either specular component excluded (SCE) or specular component included (SCI) mode. The aperture of the X-Rite units was set to 4mm—that of MMA’s current spectrophotometer—andthe Konica Minolta units were set to 8mm as they exhibited a range of apertures and, in some cases, were not adjustable.

Sanderson_1 — X-Rite Digital SG ColorChecker. Image courtesy of X-Rite

To determine an appropriate replacement, several reference standards and sample objects were tested with the seven spectrophotometers. The reference standards tested were obtained directly from X-Rite that is about to release a new Digital SG ColorChecker. The new target will include the same colors as the existing one but will utilize new pigments for some colors. For this comparative study, MMA obtained samples of the new standards to assemble its own large-format color checker. Ceramic BCRA calibrationcolor tiles were also tested as well as objects with varied surface qualities—chromogenic photographic prints (glossy and matte), watercolorpaper, textiles, and paintings. Five readings were taken and averaged for each spot tested; the units were lifted and repositioned before each measurement to account for a margin of error in positioning when monitoring color shift in objects over time using a spectrophotometer. Mylar® templates were created to facilitate positioning of the meters. All testing was completed by a single operator and resulted in approximately 12,000 readings!
To evaluate the variation in measurement between spectrophotometers, MMA’s X-Rite 968 was used as a master and delta E values were calculated for each of the 140 X-Rite color references. Sanderson summarized the results of this comparative study as follows. Meters with a 0/45 geometry produced readings with the closest match to the unit currently in use, which was not surprising as both are 0/45 instruments. When operated in SCE mode to exclude specular reflectance, the integrated spherical instruments fared worse than the 0/45. The easiest-to-use instruments were lightweight with built-in crosshair targets to facilitate alignment with a template. Finally, Sanderson introduced the concept of acceptable tolerance meaning that the operator should simplify the use of spectrophotometric readings by using a single instrument with a single set of standards. During the Q&A session that followed this presentation, a member of the audience asked which spectrophotometer MMA ultimately selected. Sanderson responded that the X-Rite eXact was selected for several reasons: it is lightweight; it produces data reasonably consistent with MMA’s existing spectrophotometer (understanding that data translation will be necessary regardless of which instrument is chosen); and long-term support from the manufacturer as well as continuity in data and software.

Sanderson_2 — X-Rite eXact spectrophotometer. Image courtesy of X-Rite

The presentation concluded with a discussion of areas of further research within this project, specifically continued analysis of data pertaining to the UV-radiation source found in some of the meters as well as the use of SCE settings in spherical integrated systems for more highly textured surfaces like those found in textile objects. Finally, it is a goal of MMA to complete processing of all data collected during this study and make it available to a wider audience so that it might contribute to more standardized color communication within the field of conservation and allied professions.

42nd Annual Meeting – Photographic Materials Group, May 31, “Characterization of a Surface Tarnish Found on Daguerreotypes under Shortwave Ultraviolet Radiation” by Krista Lough

Krista Lough, graduate intern in photograph conservation at the Metropolitan Museum of Art and third-year student in the Buffalo State College (BSC) program in art conservation, presented an interesting talk on the presence and potential sources a particular fluorescent tarnish found on many daguerreotypes when viewed under shortwave ultraviolet radiation. In addition to examination and photodocumentation of a set of daguerreotypes that exhibit this type of fluorescence, Lough also used Raman spectroscopy, scanning electron microscopy (SEM), and x-ray diffraction (XRD) to determine that the fluorescent tarnish is copper- and cyanide-based.
The presentation began with a summary of prior research on this subject by Lee Ann Daffner, Dan Kushel, John Messinger, and Claire Buzit Tagni. These studies corroborated Lough’s findings in characterizing the fluorescent tarnish as copper- and cyanide-based. These studies also showed that the tarnish was either removed or its fluorescence quenched when the daguerreotypes were treated with ammonium hydroxide.

Lough_1 — Daguerreotype and brass mat from study observed normal illumination (top) and UVC (bottom) to reveal fluorescent tarnish. Image courtesy of Krista Lough

Following a brief review of the phenomenon of fluorescence and its causes, Lough presented the photodocumentation of nine daguerreotypes that were examined during this study. The plates came from two sources—a private collection and a study collection at Buffalo State College—and only those from previously opened packages were examined. Lough’s research focused on determining the source of the fluorescent tarnish and its long-term effects. While the plates varied widely in condition, three primary types of fluorescent tarnish were identified: edge tarnish; rings and circles; and continuous film. The characteristic fluorescence was only observed when the plates were viewed under shortwave UV-C and not under longer wavelengths of ultraviolet radiation. Lough also noted that it was not always possible to associate fluorescent areas with tarnish perceived under visible light. Further, the greenish fluorescence was observed on the verso of some of the plates and along the verso and beveled edges and brass mats that accompanied some of the daguerreotypes. No strong connections could be made, however, between the fluorescence observed on the plates and the corresponding components of their once-sealed packages.
As part of her research methodology, Lough created a number of pure copper and silver-coated copper mock-ups. The mock-ups were treated with both potassium cyanide and sodium cyanide in an attempt to produce the same fluorescent tarnish observed in the 19^th-century daguerreotypes. Ultimately, the tarnish only formed in the mock-ups treated with sodium cyanide in areas of exposed, pure copper. The fluorescent tarnish did not form on the plates treated with potassium cyanide or where the copper mock-ups were protected by a coating of silver.

Lought_2 — Mock-ups observed under normal illumination (left) and UVC (right). Image courtesy of Krista Lough

To characterize the composition of tarnish, the mock-ups and select 19^th-century daguerreotypes were analyzed using Raman spectroscopy, SEM, and XRD. The Raman spectra obtained indicate that the composition of the tarnish was identical in all spots analyzed. SEM was used to create elemental maps of some of the tarnished areas on one of the 19^th-century daguerreotypes. A higher concentration of copper, carbon, and nitrogen and a lower concentration of silver were revealed in the areas of tarnish analyzed. Further, a higher concentration of sodium was observed in the areas surrounding the tarnish spots, perhaps an indication of previous treatment with sodium cyanide. Finally, XRD analysis of the fluorescent tarnish on the historic plate produced peaks for silver sulfide and pure silver. Unfortunately, while cyanide was identified on one of the mock-up plates, it was not found on the historic daguerreotype examined and it is thought that the quantities present may be below the detection limits of the XRD instrument.
Lough concluded the presentation with a list of daguerreotype procedures documented in historic literature that could account for the presence of cyanide: electroplating, cleaning, brightening, fixing, gilding, and engraving by galvanism. She also identified avenues for future research including investigation into whether or not the tarnish should be removed, the presence of copper cyanide on brass mats, and potential problems or affects to the daguerreotype that may arise if the tarnish remains untreated. Lough suggested documentation of the fluorescent tarnish could be used to develop a monitoring program for daguerreotype collections and potentially map trends during the examination of larger collections to determine, for instance, if a specific cyanide procedure is common to daguerreotypes from a particular period or location. In closing, Lough summarized the findings of her study in three main points: UV-C examination is a useful tool for understanding the condition of daguerreotypes; the fluorescent tarnish was positively identified as copper cyanide; and the objects exhibiting this characteristic fluorescent tarnish should be handled with caution as the tarnish is toxic.