Special Post – Microfading Workshop!

On June 26th 2014, Project Conservator Julia Sybalsky and Graduate Intern Gisella Campanelli attended the Microfading and Light Management Study Day, a half-day workshop and demonstration organized by Paul Whitmore at Yale University’s Institute for Preservation of Cultural Heritage (IPCH), and sponsored by IPCH and the Andrew W. Mellon Foundation.

After catching an early morning train from New York to West Haven, Connecticut, we arrived at Yale’s West Campus Conference Center for the Microfading and Light Management Study Day, hosted by the Institute for Preservation of Cultural Heritage. We enjoyed two presentations. The first talk, presented by Paul Whitmore, summarized the basics of microfading: what a microfade tester does, how it is constructed, and how and why one might use one. In the second, Bruce Ford, presented case studies from the National Museum of Australia in which microfading informed the revision of overly restrictive lighting guidelines. The result of his study was a cost-effective policy that protects light sensitive materials and materials of special significance while increasing access to collections in general.

These presentations were followed by an informal tabletop demonstration of the microfade tester. Paul gave us a comprehensive tour of the instrument and explained how to interpret the spectral data, whose stability is the measure of the relative permanence of the color. Tests on several of the inks from a set of “permanent” marking pens made the point that the label is not always an accurate description of stability.

A selection of topics covered in the course of the day’s presentations and demonstration are summarized below.

Background

Light has the potential to cause irreversible damage to objects. It can be especially deleterious to colorants, resulting in visible fading. Conservators understand that light-sensitive objects have a finite display life. Nowadays, collecting institutions often adopt guidelines to indicate the lighting conditions and durations of exhibitions of classes of objects (e.g. oil paintings, watercolors, metal sculpture, etc). These policies assume that objects within a class share the same, known stability. Some of those assumptions have been brought into question.

FadeExample_woodblock

Two copies of a Japanese woodblock print by Utamaro. When they were created, they were genetic identical twins, made from the same materials applied in the same way, probably by the same people. Then the two copies were separated at birth, with one image experiencing significant fading (by being exposed to light). Such experiences demonstrate the profound change in the object from light exposure, but also show that some colors, like the green on the kimono, are not very light-sensitive. Knowing the stability of the colors on an individual object, which may have no identical twins from which to gain information, is the challenge that microfading addresses.

In his presentation, Bruce discussed the way in which museums have traditionally managed this ‘display-destroy’ dilemma (table 1).

Table 1. Lighting requirements for display across three institutions

Institution Light level (lux) Display/Total (years)
Tate 80 4/8
V&A 50 2/10
CIE157 50 1/10

He argued that these guidelines are essentially based on guesswork and assumptions, and challenged this dogmatic approach by raising questions such as: How efficient are these standards? Are they cost-effective? Do they limit public access to objects of significance? Are they counter-productive? Do they exist in order to protect artifacts or to protect conservators?

Bruce proposed that the Micro-Fading Tester (MFT) can be used as a reliable tool to predict a colorant’s rate of fade over time. This information, along with an appreciation for the object’s significance, public demand, and aesthetic value, will better inform decisions about that object’s exhibition.

Sensitivity_significance

A structured significance evaluation can help prioritize conservation efforts and improve communication between conservators and other museum professionals. In this example, significance is used in a risk assessment aimed at assessing an item’s likely future demand for exhibition as well as its importance to the museum. Ref: Russell, R. and K. Winkworth. 2009. Significance 2.0 – a guide to assessing the significance of collection. Collections Council of Australia Ltd.

Microfading

Some colorants are more sensitive to light than others. But how do you know the sensitivity of a pigment or dye used on a specific artifact? The conventional ways to assess fading risks to objects come with a price. One way is to exhibit  the object and watch to see if its colors fade, either to the naked eye or by tracking the changes with a color measuring device. This approach obviously risks incurring some degree of fading in order to provide the information about the sensitivity to further light exposure. A second approach is to identify the materials present on the object, and to replicate those materials in all their detail in a sample that can then be exposed to light and evaluated. The challenge here is to identify the composition of the colored materials in every important detail, which can be very difficult for natural colorants which may have altered over time. Replicating such a substance is also not usually practical. This approach then becomes difficult and time-consuming, and it is impractical for application to a large number of objects. The last approach is to do spot testing, to shine light on a small area of color and measure whether the color is altered by that light exposure. That is the approach taken in the microfading tester, and the device has the added essential feature that it can be done so sensitively that the tested colors are not changed visibly: it is essentially nondestructive, so the presentation surfaces of objects can be tested safely.

The MFT delivers a focused 0.3mm beam of high-intensity light from a xenon lamp onto a tiny spot on the surface of the object and progressively measures any color changes that take place. In doing so, it allows a quick determination of whether an object contains light sensitive materials without need for their prior identification. The machine has two fiber optics angled at 45° degrees to the test surface. One fiber optic supplies the incoming beam from the xenon lamp. The incoming light is filtered to remove both infrared (IR) and ultraviolet (UV) radiation, which cause damage that is usually minimized in museum and gallery lighting environments. The object absorbs some of this incoming light, while the rest is reflected into a spectrophotometer via the second fiber optic. The spectrophotometer separates the wavelengths in this reflected light and produces a spectrum. As the spectrum is continuously updated during the test period, color measurements are recorded and used to calculate. ∆E, a measure of color change since the initial spectrum was collected. Any non-zero ∆E values indicate that the colorant being assayed is being altered by the light delivered. If the color does exhibit a color change during the test, the rate of that change is compared to the rate of fading of  Blue Wool standards, cloths whose fading rates are known and have been adopted as the international yardstick for color lightfastness. There are eight cloths in that scale, with Blue Wool #1 being least stable and Blue Wool #8 the most stable. “Fugitive” colors are considered to be in the Blue Wool #1-#3 range.

MicrofaderMounted

A microfading tester in use, measure the light stability of the colors in a lithograph. ©Paul Whitmore.

This incoming beam delivers light up to fifty times more intense than sunlight, exposing the tiny test area to a light dose equivalent to what the average museum object might receive over 5-10 years. By comparing the rate of increasing ∆E values in the test colorant to rates for Blue Wool standards exposed in the same way, the conservator is able to make informed predictions about the future behavior of the test material over time: will it retain its color for a long time like a Blue Wool 8, or is it more fugitive than a Blue Wool 1? To fully understand an artifact’s light sensitivity, each color on the object should be tested, and the exhibition policy for the object based on the stability of the most sensitive color.

Textile with emitted light from microfader visible on the surface.

Photomicrograph showing size of area tested with microfader light beam, here being directed onto a coarse-woven textile.

Microfade testing is considered an essentially nondestructive technique, as it does not leave a visible mark on the object. Not only is the test area minute, but more importantly, color change is monitored in real time by the operator and the experiment can be stopped if it looks as if visible change might occur. Meaningful results can be obtained without exceeding a ∆E value of 5, while we are only able to visually detect color differences in these tiny spots when the changes are larger than about 15. Damage can be avoided by observing ∆E values in real time throughout the duration of the test. The test usually runs for five minutes, but should be stopped earlier if ∆E approaches 5. There can be a temperature change of 5-10°C within the test location. This is usually inconsequential for most objects, but may require consideration for waxes, plastics, or other materials with low melting points. Paul explained that such test sites will often re-solidify on cooling without any visible damage, but the results of the test would not be reliable measures of color stability.

Benefits of Micro-fading

The advantage of using the MFT over traditional practices is that it eliminates the need for guesswork because it is measuring the sensitivity to exhibition lighting of colorants that are present on the actual object, rather than a simulation. Objects that can be micro-fade tested include paintings, prints (even through glass), manuscripts, photographs, 3D objects, textiles, and furs/taxidermy – basically any surface that one can make a color measurement on.

Fader_manuscript

Microfade testing at the National Library of Australia. ©Bruce Ford.

Fader_taxidermy

Microfade testing of taxidermy at the Horniman Museum and Garden, London, UK. ©Bruce Ford.

Fader_thru_glass

Microfade testing of Japanese prints, through glazing. Otago University, New Zealand. ©Bruce Ford.

Bruce explained that prior to revision of their lighting guidelines, the National Museum of Australia (NMA) typically displayed materials thought to be light sensitive for 2 years per decade. After a subsequent ‘resting’ period, objects would be returned to display, and the cycle repeated. Through his studies using micro-fading, Bruce was able to determine that numerous objects presumed to be light sensitive were in fact more stable than the 2 years exposed in 10 restriction implied (and could therefore be displayed for longer periods), while for a smaller number of items the same restriction was too generous. By measuring fading rates, very fugitive colorants were able to be identified and better protected without the need to restrict access across the board. By being more selective about restrictions using a combination of microfading and a structured significance assessment, the museum has been able to save thousands of dollars in the cost of exhibit changeovers.

NMA_savings

Illustration of potential cost savings using exhibit guidelines revised based on microfade testing. Green = extended display, yellow = unchanged display guidelines, red = displayed less than 2 years per decade.

The MFT can also be used in an anoxic environment to determine whether display in such conditions will have any appreciable benefits for the object in terms of color preservation. Some colorants may fade more rapidly in the absence of oxygen, for example Prussian blue and iron gall inks. Interestingly both of these examples undergo a reaction with oxygen which opposes the light-driven color loss but which cannot be measured using microfading or any other accelerated light exposure method. Again, this demonstrates how under-informed assumptions about reducing light damage can be unjustifiable and costly.

Conclusion

Data from microfading tests can supplement other information about the artifact to better inform decisions impacting an artifact’s display life. Using an evidence-based approach to manage display policies can prevent wasteful use of precious funds. Such resources can be redirected towards more needy causes.

How to Access a MFT

MFTs are available for purchase as kits at around $20K. Alternatively, one may contact a nearby colleague or institution that owns one to inquire about arranging for access. Currently, there are 24 MFTs in use worldwide. More information is available through Bruce Ford’s website, www.microfading.com.

What’s the Plan?

The research team had a good sense of the relative lightfastness of the Orasol dyes as a result of the renovation research, but how long could we expect the dyes to last inside an actual diorama environment? How could we better understand the ease of removal of the dyes from the animal hairs – is there a way to manipulate the dyes’ ability to penetrate or “fix” to the substrate? Could the dyes potentially cause the hairs to degrade faster inside the harsh diorama environment, or do they block the light and slow down damage – or both?

These questions acted as the foundation to the current collaboration and the focal point of the project research. Since beginning the project last fall, the majority of the work to date has focused on questions concerning lightfastness. The research team has decided to narrow future investigation to the Orasol line of dyes, rather than bringing new materials into the research plan. While the research team also looked into water soluble dyes, fiber reactive dyes, other metal-complex dyes, and some acid dyes, we were the most interested in applications that minimized the use of water.  Many of these alternative colorants are water-soluble and not appropriate for use on water-sensitive materials, require rinsing to remove excess dye and dye-bath residues, or their appearance during application does not represent their final color. The Orasol dyes remained the most promising among the materials available, as they lack the major drawbacks of some of the alternative colorants. The experimental work began in late summer 2014, starting with a large amount of sample preparation.

Lightfastness and Measuring Color Change

The first phase of the research plan tackles the question of how resistant the dyes are to fading – determining the lightfastness according to established standards (ASTM D4303) when applied without a binder or substrate that might interact with the dye. The testing done during the renovation project used wool flannel, an unstable substrate that also can discolor when aged, which could complicate being able to detect color change of the dye. For our current round of tests, we are replacing the wool flannel substrates with quartz plates, an inert substrate not expected to interact with the dye. The plates will be prepared according to methods used for testing in the paint industry – we’ll get into more detail about sample prep in future posts. Lightfastness test results will allow colors to be ranked and ASTM lightfastness ratings to be assigned to each dye color.

Intern Ersang Ma preparing dye for application to quartz plates

Intern Ersang Ma preparing dye for application to quartz plates.

Additionally, we will be developing an aging protocol that mimics ASTMD 4303, but more closely reflects the UV-filtered light conditions, temperature, and RH that are recorded inside of the AMNH habitat dioramas. This will give us a ranking of the dyes when exposed to an environment that is more similar to what the taxidermy is experiencing inside the diorama.

150  quartz plates with dyes dissolved in various solvents and airbrushed onto quartz plates for the first round of lightfastness testing.

150 quartz plates with dyes dissolved in various solvents and airbrushed onto quartz plates for the first round of lightfastness testing.

On going color measurements throughout both tests will let us better characterize the rate of color change – then we can give projections about how the dyes will hold up over time in our diorama lighting environment. Our initial light dosage calculations indicate a rough equivalence between 1 day of exposure in the environmental aging chamber at these test standards, and 1 year inside the most brightly lit dioramas.

We will also be looking into what impact, if any, solvent choice has on lightfastness and the rate of color change. Early testing during the renovation project suggested that not only can the color appearance of these dyes differ when they are applied in different solvents (as illustrated in the images below), but that the solvent choice may also affect lightfastness.

A 1% solution of the Orasol Red BL dye in MEK (methyl ethyl ketone). The dye is unevenly distributed and with distinct droplets. On the macro level, the swatch is a dark mauve.

A 1% solution of the Orasol Red BL dye in MEK (methyl ethyl ketone) applied to wool textile. The dye is unevenly distributed and with distinct droplets. On the macro level, the swatch is a dark mauve.

A 1% solution of the Orasol Red BL dye in methanol. The same dye delivered in methanol results in a more level film and a brighter color; the darkening you see is a product of higher hairs catching the airbrush more and getting more deposition.

A 1% solution of the Orasol Red BL dye in methanol. The same dye delivered in methanol results in a more level film and a brighter color; the darkening you see is a product of higher hairs catching the airbrush more and getting more deposition.

A 1% solution of the Orasol Red BL dye in PGME (Propylene glycol monomethyl ether). The dye seems to be pulled through the interstices of the weave.  In fact, if you flip the fabric over, the color looks the same on the front and the back.

A 1% solution of the Orasol Red BL dye in PGME (Propylene glycol monomethyl ether). The dye seems to be pulled through the interstices of the weave. In fact, if you flip the fabric over, the color looks the same on the front and the back.

Variations in how the dye is deposited on the substrate might influence the lightfastness of the dye – our initial accelerated aging testing will include dyes in five common solvents.

In addition to tests of the dye on quartz plates, we also need to test the dyes on fur in order to better understand the rate at which we might expect recolored taxidermy to fade or discolor. Accelerated aging tests will be conducted on samples of mounted fur, and the final selection of colors, solvents, and testing conditions will be based on the results from testing the quartz plate samples. From a long list of fur initially considered for testing, examples were narrowed down to only bison, fox, and deer hairs to represent wiry, slick, and hollow-haired fur-bearing mammals. We then had to develop a mounting system that could secure the fur samples against disturbance from handling and air turbulence. It was a challenge to trap both ends of every fiber so that they can be dyed in place while still being able to reliably take consistent color measurements of the same surfaces over the course of testing – hairs mustn’t dislodge because once they are dyed, a lost hair would expose the undyed hairs below and skew the color change measurements. We’ll reveal our mockups and final mount method in our post about sample preparation!

Equipment Purchases

Paul Whitmore watches Alan J. Boerke, a representative from the Q-Lab Corporation, during a training session at AMNH in February 2014.

Paul Whitmore watches Alan J. Boerke, a representative from the Q-Lab Corporation, during a training session at AMNH in February 2014.

For the lightfastness testing during the renovation project, we were able to partner with the Art Conservation Department at Buffalo State College to utilize their artificial aging chamber and spectrophotometer. In support of our current in-depth investigation, the grant funds allowed the AMNH to purchase several major pieces of equipment, including a Q-Sun Xenon Arc Accelerated Aging Test Chamber Xe-3 and an X-Rite Ci62 handheld spectrophotometer. Installation of the aging chamber posed some of greatest challenges in planning, and required extensive assistance from the museum’s plumbers, electricians, and carpenters from our facilities department. We’ll get into some the details of those challenges in a future post.

Orasol dyes and related colors

Over the last several months of planning, we’ve also discovered that it is difficult to obtain small quantities of the BASF Orasol dyes. Few retailers market them, and those that do carry stock that may be many years old. Other retailers use the Orasol name to sell related dyes manufactured by other companies. The true chemical and behavioral equivalence of these dyes is unknown – two dyes with the same name but different manufacturers may have differences in color, solubility, or lightfastness, among other traits. BASF has added and discontinued colors in their Orasol line over time – currently the line includes 26 colors. The previous testing as part of the renovation project included about half of the colors available – we are working to procure samples of all 26 colors. The upcoming lightfastness testing will include both new and old BASF Orasol dyes, as well as related non-BASF dyes – a total of 46 colors in 5 solvents.

And that’s just the lightfastness testing using the aging chamber! We’re expecting these initial cycles of testing to begin next month and continue through the fall and winter, and we’ll be making adjustments to the total number and types of samples to be tested along the way. There are some other avenues of testing we will be conducting, including investigating the rate of color change under real diorama lamps (as opposed to the xenon lamps used in the testing chamber), as well as exploring the possibility of being able to manipulate dye penetration and investigating the long-term effect of dyes on the hair itself.

Team Taxidermy!

In the last few posts, we discussed how the renovation of the diorama hall at the American Museum of Natural History led to the creation of our current grant project. We were confident in the testing we did prior to the renovation, and successfully recolored many of the faded taxidermy specimens in the hall – however, we were still left with a number of questions as a result of our research.

  • Our lightfastness testing investigated the dye’s resistance to fading in a controlled environment – but how long can we expect the dyes to last inside an actual diorama environment?
  • How can we better understand the ease of removal of the dyes from the animal hairs – is there a way to manipulate the dyes’ ability to penetrate or “fix” to the substrate?
  • Could the dyes potentially cause the hairs to degrade faster inside the harsh diorama environment, or do they block the light and slow down damage?

To tackle how to answer these questions, conservators at the American Museum of Natural History reached out to colleagues at Yale University’s Peabody Museum of Natural History and the Institute for Preservation of Cultural Heritage (IPCH) to collaborate on a grant proposal. We knew that there was a strong interest in recoloring taxidermy based on the feedback we received on presentations at the American Institute for Conservation‘s (AIC) 2012 annual meeting, the Society for the Preservation of Natural History Collections (SPNHC) 2012 annual meeting, and the International Council of Museums Committee for Conservation Natural History Working Group Newsletter (No.17, October 2012). We also submitted a survey among conservation practitioners, and the results indicated the urgent need for comprehensive research to identify additional colorants and protocols appropriate for recoloring fur in the museum context. The project partners were awarded a National Leadership Grant from the Institute of Museum and Library Services to fund three years of research to answer the questions that arose out of the restoration project. The conservators at the AMNH partnered with staff from the Peabody and IPCH to develop a robust research design for assessing the use of dyes and lead the evaluation of results. Additionally, an advisory panel of experts in the field was also created to support the team throughout the course of the project.   The project will culminate in a workshop hosted jointly with SPNHC to train conservation professionals in the use of well-understood, high-quality, affordable materials for the conservation of taxidermy. The project will also introduce standards for decision-making about treatment procedures and present a project website and resources (like this blog!) to support the care and treatment of natural history collections. The research also has the potential to transform how visual artists, especially those working with taxidermy, create and conserve their work. The main project team combines expertise from museum collections staff, conservators, and conservation scientists. Lisa Elkin, Judith Levinson, and Paul Whitmore are the Project Co-Directors.

Lisa Elkin, Chief Registrar and Director of Natural Science Collections Conservation, provides administrative oversight of all phases of the project and general administrative oversight of the project conservator, ensuring all timelines are effective, and planning activities relevant and achievable. She also provides specific oversight for all outreach activities including standards and best practices, website/workshop development and blog maintenance.

Judith Levinson

Judith Levinson

Judith Levinson, Director of Anthropology Conservation, provides oversight concerning the AMNH research program, specifically the preparation of samples and the aging and lightfastness analysis. She will also lead efforts in identifying re-coloring materials to be investigated and the substrates upon which they will be applied.

 

Paul Whitmore

Paul Whitmore

Paul Whitmore, Director, Art Conservation Research Center, provides oversight of the overall research program and its development. He will provide support concerning analysis and evaluation of results, and foster access to expertise across the Yale science departments.

 

 

Julia Sybalsky

Julia Sybalsky

Julia Sybalsky is the Project Conservator. Julia carries out all the project analysis at AMNH and Yale. She will document all findings for presentation to the project team, the advisory committee, and the field at large. She will also work with the project participants in developing content for the website, the workshop, and the blog.

 

Aniko Bezur, Wallace S. Wilson Director of Scientific Research at the Center for Conservation and Preservation at Yale University, provides guidance in the use of analytical equipment and evaluation of results.

 

Beth Nunan

Beth Nunan

Beth Nunan, Associate Conservator at AMNH (that’s me!), maintains the project blog and will assist the project conservator with sample preparation and analysis at AMNH.

 

 

Tim White, Director of Collections & Operations at the Yale Peabody Museum, ensures that the results of the project are up to the standards expected of this field and disseminated to the appropriate audiences – conservators, collections managers, taxidermists, etc.

 

Richard Kissel

Richard Kissel

Richard Kissel, Director of Public Programs at the Yale Peabody Museum, provides guidance concerning the best methods for disseminating results particularly related to social media, web and blog technologies.

 

 

Michael Anderson, Museum Preparator at the Yale Peabody Museum, stands as the resident expert on habitat dioramas and provides guidance concerning the visual impact any treatment must have.

Catherine Sease, Senior Conservator at the Yale Peabody Museum, provides guidance concerning the potential long-term impact of the proposed treatments to specimen-based collections.

The role of our external advisory committee is to review the research questions to ensure that the issues critical to working and visual properties and long terms stability are covered. Annual meetings will help provide a forum to present details concerning the program and encourage discussion of the results: whether the methods of analysis need to be adapted and whether timelines need to be re-thought. Through regular updates, including these blog posts, the committee can  monitor the overall direction of the project, review the testing conducted thus far, and provide input concerning dye application and interpretation.

Members of the external advisory committee include:

Corina Rogge

Corina Rogge

Corina Rogge, PhD., Andrew W. Mellon Research Scientist at the Museum of Fine Arts, Houston. Dr. Rogge provides a critical role of oversight concerning the research program and analysis of results. Dr. Rogge will be the point person liaising between the project team and the committee and will have the most regular contact with the project team.

 

Catherine Hawks

Catherine Hawks

Catherine Hawks, Museum Conservator, National Museum of Natural History. Ms. Hawks is a renowned natural science conservator and will provide guidance concerning the potential long-term impact of the proposed treatments to specimen based collections.

 

 

GeorgeD_MTLion

George Dante

George Dante, Master Taxidermist. Mr. Dante was the taxidermist on staff for the AMNH diorama renovation project. He will provide insight concerning the suitability of the various dyes for treatment and will assist in disseminating results to the world of professional taxidermists as an effort to improve current methods and practices in this professional community.

 

Stephen Quinn

Stephen Quinn

Stephen Quinn, Diorama Historian and Artist. Mr. Quinn is the authority on habitat dioramas and was the project director of the AMNH diorama renovation. He will provide insights into the methods and materials used in constructing historic taxidermy and how the proposed treatments could be influenced as such.

 

 

Jane Pickering

Jane Pickering

Jane Pickering, Executive Director, Harvard Museums of Science and Culture. Ms. Pickering will provide the voice for public programming, education and exhibition. She will guarantee dissemination of the results to these communities and will provide guidance in the planning and development of the workshop and website.

 

 

We are excited to be collaborating with so many new partners! This diverse team of specialists has helped to guide the creation of a well thought-out research design and methodology that ensures key issues can be effectively addressed – more on this research plan in the next post!

A Horse of a Different Color – researching colorants for recoloring taxidermy

For the 2011-2012 renovation of the Bernard Family Hall of North American Mammals dioramas, we were limited by the need for high lightfastness (resistance to fading), in situ treatment considerations, health and safety requirements, and reversibility/retreatability, so the project conservators looked to materials already in use in our profession (see previous posts for more details on this project). The Orasol® dyes seemed like a good alternative to the acrylic paint favored by the project taxidermist. Orasol® dyes (Ciba-Geigy; currently marketed by BASF for coatings and printing inks) are commercially available metal complex dyes that cannot be dissolved in water, but can be dissolved in many common organic solvents such as ethanol. They can be applied without salts or peroxides (which can be acidic), and require no rinsing, making them useful for in situ treatment. They are manufactured in a palette of 26 colors, which was enough to mix the range of tones needed for the North American Mammals. They are also generally approved by the conservation community and are commonly used in furniture and wood stains, as well as for tinting epoxy and other resins used for fills.

A word on dyes:

A dye is a substance that has an affinity to the substrate (in our case, the hair of the taxidermy mount) to which it is applied. In contrast, a pigment is generally insoluble and has no affinity for the substrate.

A typical dye molecule is composed of different chemical groups, each responsible for a specific property of the dye:

  1. Chromophore – color producing portion
  1. Auxochrome – influences the intensity of the color and provides the site at which the dye chemically bonds with the fiber (hydrogen, ionic, or dipole-dipole interactions with the substrate).
  1. Solubilizing group – allows the dye molecule to be soluble in a given solvent so it is capable of reacting with the fiber.
Typical dye molecule (from Synthetic Dyes for Natural Fibers. Knutson, Linda. 1982)

Typical dye molecule (from Synthetic Dyes for Natural Fibers, Linda Knutson. 1982)

Metal complex dyes are made of a transition metal ion such as chromium, copper, or cobalt complexed to two symmetrical dye molecules (chromophore and auxochrome). In general, members of this group have better lightfastness (resistance to fading) compared to other dyes due to the stability of the chelated complex and their large particle size; this, along with their working properties, has been the basis for their past use in conservation.

To determine if the dyes met all of our needs for the project, we developed some tests to compare the acrylic paints to the Orasol® dyes. The conservators worked closely with the taxidermist and partnered with outside conservation scientists to test the materials against these necessary criteria: minimal physical alteration to the hairs, retreatability/reversibility, and high lightfastness.

The physical appearance of bison hair samples colored with acrylic paint and ones colored using Orasol® dyes was examined using normal light as well as scanning electron microscopy (SEM). At first look, all of the colored samples appeared somewhat similar. The acrylic paints produced a matted and stiff feel, whereas the Orasol® dyes produced a more natural look and feel. The SEM images showed us that the binder in the acrylic paints covered the hair cuticle unevenly, creating a non-cohesive coating around the hair with some visible peeling and lifting. The Orasol® dyes were only just visible on the hair fibers and did not appear to cover or coat the hair shaft.

The surface of bison hairs imaged using scanning electron microscopy. From left to right: control (no colorant), acrylic paint, Orasol dye.

The surface of bison hairs imaged using scanning electron microscopy. From left to right: control (no colorant), acrylic paint, Orasol dye.

The taxidermist also found that the Orasol® dyes could be reduced or removed entirely when wiped or rinsed with ethanol after application. Although initially taken aback by this revelation, we quickly recognized the potential for reversibility, as well as the ability to produce special effects, such as localized reduction or removal of color to achieve special effects.

Project taxidermist reduces dye from a practice skin.

Project taxidermist George Dante reduces dye from a practice skin.

Metal complex dyes are generally regarded as having a high lightfastness. However, chromophore and auxochrome structures vary, making some dye colors more susceptible to fading. In their product literature, the manufacturer reports a definite range in both lightfastness and solubility from color to color.

Orasol dye lightfastness ratings according to manufacturer.

Orasol dye lightfastness ratings according to manufacturer.

These ratings are based on their use in printing ink, and the tests were conducted with two different binders (nitrocellulose and vinyl acetate) which produced significantly different results. To be able to judge the lightfastness of the Orasol® dyes when used on taxidermy, it was necessary to conduct our own tests without any binding media.

 The lightfastness of the dyes was tested using accelerated light-aging following the ASTM D4303 Standard Test Methods for Lightfastness of Colorants Used in Artists’ Coloring Materials. Test swatches were produced by airbrushing a 1% solution of dye dissolved in ethanol onto unbleached 100% wool as well as swatches of bleached bison fur. As a flat substrate of keratin fibers, the wool textile was chosen as a reasonable substrate to measure color changes using a spectrophotometer. Details about the testing procedure will not be listed here, but will be covered in subsequent posts as continued lightfastness testing is part of the current research program.

Conservation Fellows Julia Sybalsky and Rebecca Pollak prep swatches of Orasol dye for testing.

Conservation Fellows Julia Sybalsky and Rebecca Pollak prep swatches of Orasol dye for testing.

The ASTM protocol requires exposure of test materials to a broad spectrum of light that includes ultraviolet (UV) radiation. Since new lights in the diorama are filtered to exclude this particularly damaging light, the test helped us develop a worst-case scenario for assessing the lightfastness of the dyes.

Real-time monitoring of cumulative light exposure is continuing inside the bison diorama. Orasol dyes are exposed in situ alongside Blue Wool reference standards out of sight of visitors. At the same time, portions of the bison have been sprayed with dye mixtures and masked to permit direct comparison of exposed and unexposed areas of restoration.

Strategically placed dyed swatches and a blue wool card were placed inside the bison diorama (hidden from view), and sections of the dyed bison were covered for side-by-side comparison.

Strategically placed dyed swatches and a blue wool card were placed inside the bison diorama (hidden from view), and sections of the dyed bison were covered for side-by-side comparison.

Our lightfastness tests identified the most stable of the dye colors, allowing us to be picky about which shades could be used for the diorama taxidermy. The reversibility and retreatability of the dyes also played a major factor when deciding to use them on specimens in dioramas with higher light levels, with the understanding that fading will occur in time. The AMNH conservation and exhibition team was able to successfully recolor many of the faded specimens in the Bernard Family Hall of North American Mammals.

Coyote, before and after recoloring.

Coyote, before and after recoloring.

The dye research we did as part of the renovation generated numerous new questions, which fell into three main topics:

Lightfastness – While our previous testing did effectively establish a lightfastness ranking among the Orasol colors, it didn’t answer one of the questions we were asked the most often – “Ok, we know that the dyes in the brighter dioramas are eventually going to fade… how long will they last?” By developing a test procedure that mirrors the UV-filtered lighting environment in the dioramas , we will get enough information to be able to create a probable lifespan for these materials when used in treatment.

Penetration/Fixation – While the ease of dye removal was beneficial in the 2011-2012 recoloring treatments, in other contexts you might want a greater fixation or penetration of the dye. We want to understand ways we could achieve and manipulate that “fixability”, as well as knowing if those variations impact the dyes working properties and lightfastness.

Substrate Degradation – Finally, we want to better understand whether or not the use of recoloring materials like the Orasol dyes causes the colored animal hairs to degrade faster than normal, or do they act as a protectant and slow down light damage?

These topics acted as a starting point for the research plan for the current project: Recoloring Faded Taxidermy: Research into the Properties and Applicability of Dye Materials for Conservation Treatment, the details of which will have to wait until the next post!

Renovation of the Bernard Family Hall of North American Mammals Part II: Unique Challenges in Restoring Faded Taxidermy

Badly in need of restoration after over 70 years of exposure to high light levels, temperatures, and fluctuations in relative humidity, the iconic habitat dioramas in the Bernard Family Hall of North American Mammals were renovated in 2011-12. Among the most significant problems was fading observed in the taxidermy specimens.

Some members of the diorama renovation team: Museum Exhibition Project Manager: Stephen Quinn. Museum conservators: Judith Levinson, Lisa Elkin, Elizabeth Nunan. Conservation Fellows: Julia Sybalsky, Bethany Palumbo. Museum artists: Richard Webber, Joi Bittle-Knight. Project Taxidermist: George Dante AMNH/E.Nunan

Some members of the diorama renovation team: (clockwise from upper left) Director of Natural Science Conservation Lisa Elkin, Museum Exhibition Project Manager Stephen Quinn, Assistant Conservator Elizabeth Nunan, Project Taxidermist George Dante, Director of Anthropology Conservation Judith Levinson, Museum exhibit preparator Joi Bittle-Knight, Museum exhibit preparator Richard Webber, Conservation Fellows Julia Sybalsky and Bethany Palumbo.
©AMNH/E.Nunan

 

The diorama renovation team (curators, conservators and conservation scientists, exhibit preparators, taxidermist) faced a number of challenges in choosing an appropriate colorant to restore the faded taxidermy in the dioramas. One of the most immediate difficulties was the short project timeline, which limited the type and extent of research that could be done. There was only one year for all of the renovation work to take place, from start to finish, with 45 dioramas and over 100 taxidermy specimens. A maximum of only 2 months within that year could be allotted for research and testing of possible colorants for the faded mammals.

In addition to the limited research period, there were several other critical factors that restricted the materials that could be considered for re-coloring.

High light levels

Even with the new energy efficient lights, the naturalistic lighting design in each diorama did not allow us to reduce light levels to what is generally considered acceptable for museum collections. The highest recorded light levels are 65 footcandles (fc) on the top of the mountain goat and 50 fc at the head of the cow in the bison diorama, whereas the recommended level for fur at the Museum is 5 foot candles. Therefore, even with somewhat reduced light exposure, it was clear from the outset that any colorant considered for use would have to have high light-fastness ratings to limit fading under the harsh diorama conditions.

Light levels in the Mountain Goat diorama. ©AMNH/E.Nunan

Light levels in the Mountain Goat diorama.
©AMNH/E.Nunan

Treatment in situ

Because the larger taxidermy mounts had to be treated in situ, custom built platforms to avoid crushing the fragile foreground materials were required to provide safe access. Washing or rinsing excess coloring materials from the specimens would not be possible. Ease of preparation, application, and clean up were all important considerations when choosing a colorant.

 Installing platforms inside dioramas in the Bernard Family Hall of North American Mammals ©AMNH/E.Nunan


Installing platforms inside dioramas in the Bernard Family Hall of North American Mammals
©AMNH/E.Nunan

Health and Safety

The use of certain solvents was restricted because possibilities for effective fume extraction inside the dioramas were limited. Additionally, because half of the exhibition hall was required to remain open to the public over the duration of the project, control of solvent fumes was critical.

 Project taxidermist and artist wearing respirators during recoloring. ©AMNH/E.Nunan


Project taxidermist and artist wearing respirators during recoloring.
©AMNH/E.Nunan

Reversibility/Retreatability

Because the dioramas would probably not be renovated again for at least 25 years due to associated costs, favorable aging characteristics, reversibility and ease of future retreatment were important factors in choosing recoloring materials. The colorants selected should not cause the hairs to clump or mat, and if not fully reversible they should not prevent future recoloring projects on these irreplaceable taxidermy mounts.

Investigation of the conservation literature on contemporary methods for coloring taxidermy revealed few references. Through personal correspondence, some museums reported success recoloring some of their taxidermy mounts using Clairol commercial hair dye, but their situation allowed for the removal of the specimens from the diorama for treatment, and the long-term stability of those dyes are not known. Other recent studies investigated fiber-reactive dyes for feather recoloring, but the approach was ruled out due to concerns about water-based treatments having an adverse effect on the tanned taxidermy hides, as well as the long-term effects of the acidic or basic dye residues.

Water and solvent-based acrylic paints are commonly used among contemporary taxidermists. When used inside habitat dioramas, reversing acrylic paints for retreatment would be very problematic. Also, due to their low glass transition temperature, it is possible that the paints would remain soft in the heat of the diorama lamps, entrapping dust and hindering future cleaning.

The project taxidermist’s familiarity with commercially available acrylic paints and his skill with airbrushing played a tremendous factor in determining what other colorants would be considered.

 An echidna mount recolored by taxidermists at Wildlife Preservations, Inc using acrylic airbrush paints. ©G. Dante/Wildlife Preservations, Inc.


An echidna mount restored and recolored by taxidermists at Wildlife Preservations, Inc using acrylic airbrush paints.
©G. Dante/Wildlife Preservations, Inc.

His method for restoring faded specimens consisted of layered airbrush applications with constant grooming throughout the process in order to control the hue and intensity of the color. Any alternative colorant would need to be applied in a similar manner, in order to fully utilize the taxidermist’s skill in this method, and to meet the tight project deadline.

 Taxidermist George Dante recoloring a bison mount. ©AMNH/E.Nunan


Taxidermist George Dante recoloring a bison mount.
©AMNH/E.Nunan

The next post will discuss the colorants that the research team chose, as well as the tests conducted to determine whether they met the necessary criteria for minimal alteration to hairs, high lightfastness, and retreatability/reversibility.

Renovation of the Bernard Family Hall of North American Mammals, Part I: What is a habitat diorama?

In 2011-12, the American Museum of Natural History undertook an ambitious program of renovation to the 45 habitat dioramas in the Bernard Family Hall of North American Mammals.  It was important that the unique features of each diorama be preserved throughout the renovation project, which played a role in deciding what kind of materials could be used for recoloring the faded taxidermy. This post summarizes how the dioramas were constructed – full details on the creation and significance of the Museum’s dioramas are beautifully illustrated in Stephen Quinn’s, Windows on Nature: The Great Habitat Dioramas of the American Museum of Natural History.

Some of the earliest collections at the Museum were taxidermy, and the evolution of the diorama was a natural development in the tradition of using art to teach science. Within the museum, dioramas were created to promote the awareness of wildlife and so-called ‘primitive cultures’ as finite. They were also used to stir concern for the populations and habitats that were threatened by unregulated development and hunting. Fusing art and science, these habitat dioramas depict specific locations and exhibit anatomically correct mounted specimens in their natural habitat.

The wolf diorama in the Bernard Family Hall of North American Mammals ©AMNH/D.Finnin

The original creation of the dioramas was a group effort, combining the skills of artists and scientists to illustrate the complex relationships between animals and their environment. Along with the Museum’s curators, they conducted extensive research, visiting each site to draw reference sketches, take photographs, and collect specimens for exhibit. Once back at the museum, every detail of the scene was painstakingly recreated. Careful positioning of specific lighting combinations illuminated the background paintings to create a particular season and time of day in the depicted location, with naturally posed taxidermy among site-specific plants and foreground materials.

 Fred Scherer and James Perry Wilson painting the background of the bison and pronghorn diorama, while George Mason installs grass in the foreground. (S.Quinn, Windows on Nature) ©AMNH/Library 296655


Fred Scherer and James Perry Wilson paint the background of the bison and pronghorn diorama, while George Mason installs grass in the foreground. (S.Quinn, Windows on Nature)
©AMNH/Library 296655

The dioramas at the American Museum of Natural History are the ultimate mixed-media artifact.  They are made of three main elements: a background painting, foreground materials, and mounted taxidermy specimens. The partial dome-shaped enclosure is created using vertical angle-iron beams and heavy wire mesh. This framework supports layers of plaster, onto which the canvas background painting is attached using a white lead and oil mixture as adhesive. Access to the dioramas is difficult and can only be achieved by removing the front panes of glass or, in some cases, is attained by narrow ladders on the interior extending from the light box to the diorama floor.

The background paintings in the habitat dioramas were examples of the highest form of wildlife artistry in their day, and many consider those in the Bernard Family Hall of North American Mammals to be the most accomplished of their kind. The curved background painting is essential to the overall illusion of space, distance and environment.  It draws on Renaissance techniques such as under-painting, plotting perspective and transferring images with grids. Painters of note included James Perry Wilson, Frances Lee Jaques and Charles S. Chapman. Wilson described his diorama work as “art to conceal art’, in other words, art intended to imitate nature so closely that the artist’s role is not visible (Quinn, 2006).

 James Perry Wilson field sketching at Devil's Tower, Wyoming (1942) ©AMNH/Library


James Perry Wilson field sketching at Devil’s Tower, Wyoming (1942)
©AMNH/Library

The floor of the diorama was built up to the needed height with an underlying structure of wooden beams, over which wire screening was formed to create the desired topography. Features of the landscape were constructed over the wire screening with a mixture composed of plaster, dextrin, whiting, and asbestos fibers.  Plant materials were generally made from painted cotton or paper, sometimes flocked or modeled with wax.

 George Mason laying down wire mesh over the wood structure to create the ground terrain in the bison and pronghorn antelope diorama, 1942. (S.Quinn, Windows on Nature) ©AMNH/Library


George Mason laying down wire mesh over the wood structure to create the ground terrain in the bison and pronghorn antelope diorama, 1942. (S.Quinn, Windows on Nature)
©AMNH/Library

Broad leaves were made from vacu-formed acetate sheet. Snow was created using combinations of plaster, sand, cotton batting and plastics.  A limited number of real botanical specimens, such as grasses, evergreen branches, mosses, and leaves for ground litter, were collected, sometimes chemically treated with preservatives, and then installed. The mammal specimens were mounted in the museum following procedures developed by Carl Akeley in earlier decades, details of which are also discussed in Windows on Nature (Quinn, 2006). The larger taxidermy specimens are mounted into the diorama floors, and thus cannot be removed for treatment.  Many of the smaller specimens, however, are able to be removed.

 The plant-making process for dogwood flower production, 1933. (S.Quinn, Windows on Nature) ©AMNH/Library


The plant-making process for dogwood flower production, 1933. (S.Quinn, Windows on Nature)
©AMNH/Library

A large glass panel serves as the front face of the diorama, and is angled slightly to prevent reflection.  A separated light box with fixtures for interior illumination is located above the enclosure. The original lighting scheme from the early 1940’s is known to have included large theatrical lights.  Lighting revisions shortly thereafter, in the 1950s, resulted in a combination of fluorescent and incandescent fixtures.  This scenario caused a number of unsurprising problems.  Temperature inside the dioramas was elevated, often reaching the high 80’s °F.  The relative humidity was low, with daily and seasonal fluctuations.  Light levels were far higher than is recommended for museum collections and, until recently, lamps were not screened for ultraviolet emissions.  These conditions resulted in deterioration, desiccation, and fading of most exhibit materials.

 Lighting technician Arthur Scharf adjust lights in the Timberline group diorama in the Hall of North American Forests, 1954. ©AMNH/Library 323121


Lighting technician Arthur Scharf adjust lights in the Timberline group diorama in the Hall of North American Forests, 1954.
©AMNH/Library 323121

Informed by a 2003 conservation survey of the dioramas in the Museum’s Akeley Hall of African Mammals undertaken at the museum, testing had demonstrated that it was possible to reduce heat and light levels inside the dioramas while maintaining the desired visual appearance through the use of energy-efficient lamps.

In 2010, as a result of the American Museum’s participation in a citywide effort to decrease energy consumption, funding was provided to replace the diorama lights with more energy-efficient fixtures. The goal of the re-lamping project was to achieve a 50% reduction in electric power consumption. Retrofit fixtures were researched and chosen by an outside lighting design firm to reproduce the visual appearance of the original design, using a combination of energy efficient fluorescent bulbs for indirect lighting and LED flood lights and metal halide spot fixtures as accent lights.  All new lighting fixtures are filtered for UV emissions.

The re-lamping project provided the impetus for a broader renovation of the Hall of North American Mammals.  The renovation team began to explore possible methods of restoring naturalistic color to specimens that had become faded and desiccated in the previous damaging lighting environment in hopes of extending their exhibit life.

Just as the dioramas’ fabrication was necessarily achieved through collaboration, this conservation effort also involved a diverse team of participants, including curators, objects and paintings conservators, exhibition department staff, outside scientists, and a master taxidermist.

The next post will examine the many factors that influenced how we decided what recoloring materials to research and test.

 

AMNH/D.Finnin

Introducing the Recoloring Taxidermy Research Project

In 2013, the American Museum of Natural History and Yale University’s Institute for the Preservation of Cultural Heritage and the Peabody Museum of Natural History were awarded an Institute for Museum and Library Services‘ (IMLS) National Leadership Grant to fund a three-year project devoted to the development of best practices for recoloring faded mammal taxidermy mounts, especially those in habitat dioramas: Recoloring Faded Taxidermy: Research into the Properties and Applicability of Dye Materials for Conservation Treatment.

After years of display under bright lights, and harsh temperatures and humidity, many taxidermy mounts have become discolored and faded. Techniques for restoring the lost colors of damaged natural history collections are limited and under-researched. This knowledge gap puts at risk collections of great educational value, especially as some historical specimens represent species that are endangered, if not already extinct.

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The project conservators are interested in developing re-coloring methods that would minimally alter the texture or sheen of hair and fur, and could be as reversible or re-treatable as possible.

This research will foster cross-disciplinary partnerships between conservators and scientists with varying forms of expertise, helping to bridge the institutional gap between natural history, art, and history museums and collections.

The IMLS-funded project will build upon promising results from a pilot study conducted by the Museum into the use of certain dyes, such as those used in certain specialized printing inks, to recolor taxidermy hair and fur. The next few posts will present the results of the restoration project that resulted in the dramatic restoration of the faded specimens in the habitat dioramas in the Museum’s Bernard Family Hall of North American Mammals.

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The findings from the study, which the Museum conservators presented at 2012 annual meetings of the Society for the Preservation of Natural History Collections (SPNHC) and the American Institute for Conservation (AIC) and published in the October 2012 International Committee of Museum, Natural History Collections Working Group Newsletter, were received with immense interest by practitioners and researchers alike. Together with results from a national survey among conservation professionals, it was evident that there was a strong need for comprehensive research to explore additional materials and discover an appropriate method for recoloring faded taxidermy in museum collections.