It’s All In the Preparation: Part 1

As earlier posts have mentioned, the first phase of our research aims to establish the lightfastness of the Orasol® and similar Sorasolve metal-complex solvent dyes in isolation‒ that is, in the absence of a binder, and without a chemically active substrate that could potentially influence the behavior of the dyes or interfere with the measurement of color change. To accomplish this we needed a substrate for the dye film that would not be altered physically or chemically by the accelerated aging exposure and would not interfere with our reflectance measurements (reflectance measurements will be discussed further in up-coming posts). The required substrate would need to be:

1.  Optically pure.

Any color or visual irregularities in a substrate would affect our color measurements, and impede an accurate calculation of the dyes’ lightfastness.

2. Durable.

The substrate needs to withstand a degree of handling throughout its use. For example, in one test cycle, the samples are measured for color change 8 times, in addition to before-, during-, and after-treatment photography.

3. Chemically inert.

The substrate must not be altered physically or chemically by the accelerated aging process, to ensure that it does not discolor (impeding accurate measurement of color change in the dye itself) or produce reaction products that could potentially alter the behavior of the dye.

Before making our final choice, we considered and rejected several candidates:

pink dye on wool

BASF dye Pink 478 (CIGN Solvent Red 127) sprayed on wool textile substrate. Although wool readily accepts dye, it was not chosen as the substrate because of its chemical instability during accelerated aging. Note also that the color of the dye is different depending on solvent. Solvent, top to bottom: acetone, ethyl acetate, ethanol, isopropanol, PGME. AMNH/F. Ritchie

Wool textile: inexpensive, readily available, and resilient to handling. It has the great benefit of accepting the dye in a manner very similar to the fur/hair on our taxidermy specimens because it is made from the same material, keratin fiber. However, it is not chemically inert, and is known to bleach or yellow during accelerated aging.

Acid-free paper: durable and inexpensive, but, like wool, is not chemically inert and may undergo color change or influence the stability of the applied dye. In addition, it accepts the dye solutions in a manner quite different from hair/fur, as they are readily absorbed deep into the sheet.

Glass slides or plates: much more chemically stable than wool or paper, though they may still produce reaction products in high temperatures and humidity. Dye applied to glass sits on the surface, similar to keratin fiber. Glass is inexpensive, but could be cleaned and reused if necessary. It is, of course, more fragile than wool or paper.

Ultimately we decided to use thin quartz plates, because they best fulfill our optical, physical, and chemical requirements for a substrate. Quartz plates consist of pure silicon dioxide (SiO2). They are not only optically pure (being transparent and colorless) and have a high damage threshold; they are also non-absorbent and reusable. However, as we came to appreciate, they are typically used in very sensitive research applications, which require high standards of dimensional exactness and chemical/optical purity. As such, they aren’t cheap. Finding affordable quartz plates was very challenging, and eventually took us to a Chinese company that was able to provide us with custom-cut plates that easily met the needs of our project, without the cost that accompanies the exacting standards required by other research applications.

Drawing on the procedure outlined in the ASTM D4303 standard, our testing of each dye solution and set of lighting conditions uses three replicate samples (A, B, and C). Two plates (A and B) are exposed in the aging chamber during the test cycle, and the third (C) is held in dark storage as a control. Throughout each test cycle, color measurements are taken periodically from each replicate. Each plate is measured in three locations, and these results are averaged to produce an overall measurement for that sample at that time index.

Having selected a transparent substrate, it was necessary for us to then identify a material to place behind our samples during our reflectance measurements and accelerated aging cycles. For the former, a standard white backing material was needed — something opaque (to eliminate any influence on the measurement from the tabletop or work surface behind this backing), and either durable or easily replaced. It would also need to be extremely white (i.e. with a uniform high reflectance throughout the visible spectrum) so that it would reflect the light transmitted through the sample back up into our reflectance spectrophotometer without distorting the spectrum of the dye. We chose to use plain white nitrocellulose membrane filters stacked three layers deep to ensure opacity. While a white ceramic tile could also have been used, we felt that the membrane filters would be more easily incorporated into the wooden jig that we are using to standardize our measurement locations.

jig with sample__1

Jig built for the project to hold quartz plate dye samples during color measurements. Note the white nitrocellulose film used to back samples. AMNH/F. Ritchie

For the same reason that a white backing material is helpful in color measurement, it would be problematic in our accelerated aging exposures: a white surface would act as a mirror, reflecting light from the xenon lamp that had already passed through the sample back up toward the plate. This would be exposing the dye films twice, once by direct exposure of the lamps, and a second time by reflected light from below, increasing the light exposure dose by some unknown percentage. This would make our determination of a rough equivalence between accelerated and real time aging periods in our dioramas more difficult. Eliminating the backing altogether would have the same effect: the plates would rest directly on our reflective aluminum sample holders. We needed to identify a material that would absorb the light transmitted through the sample plates but also would withstand the extreme environment within the accelerated aging chamber. We would need to use a black backing inside the chamber.

To realize this light-absorbing backing, we initially lined our aluminum sample holders with black archival matte board. We also added bumpers along the edges of the backing to create a small space for air circulation between the board and the plates, which helps with heat dissipation. Unfortunately, we discovered that the matte board generated a sticky condensate on the underside of the plates during aging. We altered our design to instead use black textile masks and corrugated blue board. These have proven to be free of the condensate problem of the matte board. The masks slowly fade during our exposures that include UV radiation, so we designed our sample mounts in such a way that new masks can be inserted when replacement is needed.

black panel_plate_holder

Clockwise: Quartz plate without dye, sample backing of black textile mask with cardboard bumpers covered in black textile mask, metal sample holder. AMNH/F. Ritchie

sample holders

Top: Dye samples resting on black backing. Bottom: Dye samples assembled in sample holder, ready for testing. AMNH/F. Ritchie

 

 

 

 

 

 

Part Two will describe how we prepare the quartz plate dye samples.

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The Dye Is Cast

The initial sample set undergoing accelerated aging in our Q-SUN chamber is expected to be the largest. It includes all of the Orasol dyes that we have been able to acquire to date from the manufacturer BASF and retail supplier Kremer Pigments, as well as Sorasolve dyes available from Museum Services Corporation (MSC). This post includes a listing of all of our dye samples. For a comprehensive concordance of materials by manufacturer, current and former product names, and Colour Index Generic Names (CIGN), please see the table at the end of the post.

Orasol dyes, manufactured by and available from BASF

BASF does not sell small quantities of its product directly to consumers, but samples may be requested from the company for testing purposes. Materials obtained this way are understood to be of relatively recent production.

  • Orasol® Red 330 (CIGN Solvent Red 130)
  • Orasol® Red 335 (CIGN Solvent Red 122)
  • Orasol® Red 355 (CIGN Solvent Red 119)
  • Orasol® Red 363 (CIGN Solvent Red 125)
  • Orasol® Red 365 (CIGN Solvent Red 160)
  • Orasol® Red 395 (CIGN Solvent Red 122)
  • Orasol® Red 471 (CIGN Solvent Red 118)
  • Orasol® Pink 478 (CIGN Solvent Red 127)
  • Orasol® Orange 245 (CIGN Solvent Orange 56)
  • Orasol® Orange 247 (CIGN Solvent Orange 11)
  • Orasol® Orange 251 (CIGN Solvent Orange 54)
  • Orasol® Orange 272 (CIGN Solvent Orange 99)
  • Orasol® Yellow 081 (CIGN Solvent Yellow 79)
  • Orasol® Yellow 141 (CIGN Solvent Yellow 81)
  • Orasol® Yellow 152 (CIGN Solvent Yellow 88)
  • Orasol® Yellow 157 (CIGN Solvent Yellow 82)
  • Orasol® Yellow 190 (CIGN Solvent Yellow 89)
  • Orasol® Blue 825 (CIGN Solvent Blue 67)
  • Orasol® Blue 855 (CIGN Solvent Blue 70)
  • Orasol® Brown 324 (CIGN Solvent Brown 43)
  • Orasol® Brown 326 (CIGN Solvent Brown 44)
  • Orasol® Black X45 (CIGN Solvent Black 28)
  • Orasol® Black X51 (CIGN Solvent Black 27)
  • Orasol® Black X55 (CIGN Solvent Black 29)

Orasol dyes, manufactured by BASF, and available from Kremer Pigments

Kremer sells small quantities of BASF Orasol dyes retail. To do so, they purchase dyes in bulk from BASF and warehouse the stock until it is sold. As a result, dyes purchased from Kremer have an unknown production and storage history. Orasol products listed in Kremer’s product catalog are identified using both old and newer Orasol naming systems, reflecting the name in use by the manufacturer at the time Kremer made its purchase from BASF.

  • Orasol® Red 395 (CIGN Solvent Red 122)
  • Orasol® Orange 247 (CIGN Solvent Orange 11)
  • Orasol® Yellow 152 (CIGN Solvent Yellow 88)
  • Orasol® Yellow 4GN (CIGN Solvent Yellow 146)
  • Orasol® Yellow 2RLN (CIGN Solvent Yellow 89)
  • Orasol® Blue 825 (CIGN Solvent Blue 67)
  • Orasol® Brown 324 (CIGN Solvent Brown 43)

Sorasolve dyes, manufactured/supplied by First Source Worldwide LLC, and available from Museum Services Corporation (MSC)

Museum Service Corporation’s retail product-catalog lists their metal-complex solvent dyes using the old BASF naming system for the Orasol® brand; however, the dyes are supplied to MSC under the brand name Sorasolve by First Source Worldwide LLC, an American chemical company based in Neenah, Wisconsin. Orasol® and Sorasolve dyes with the same Colour Index Generic Name share an essential colorant with the same chemical constitution.

  • Yellow 2RLN (Sorasolve/CIGN Solvent Yellow 89)
  • Yellow 4GN (Sorasolve/CIGN Solvent Yellow 146)
  • Yellow 2GLN (Sorasolve/CIGN Solvent Yellow 88)
  • Orange G (Sorasolve/CIGN Solvent Orange 11)
  • Red BL (Sorasolve/CIGN Solvent Red 122)
  • Red G (Sorasolve/CIGN Solvent Red 125)
  • Pink 5BLG (Sorasolve/CIGN Solvent Red 127)
  • Blue GN (Sorasolve/CIGN Solvent Blue 67)
  • Brown 2GL (Sorasolve/CIGN Solvent Brown 42)
  • Brown 2RL (Sorasolve/CIGN Solvent Brown 43)
  • Brown 6RL (Sorasolve/CIGN Solvent Brown 44)
  • Black CN (Sorasolve/CIGN Solvent Black 28)
  • Black RLI (Sorasolve/CIGN Solvent Black 29)

We have characterized all of these dyes using fourier transform infrared spectroscopy (FTIR). Our results confirm that samples of old and new Orasol® dyes, as well as the related Sorasolve dyes, have very similar infrared spectra (see image below).

Yellow 89

FTIR spectra for Solvent Yellow 89 samples acquired from BASF (purple line), Kremer (blue line), and MSC (red line). Note the likeness between spectra, indicating that the three dyes sold by three companies under the same CIGN are chemically very similar, if not the same.

All of these dyes are soluble in a wide selection of solvents. As mentioned previously, during dye testing conducted in conjunction with the renovation of the dioramas in the Jill and Lewis Bernard Family Hall of North American Mammals, we observed that solvent choice can have subtle effects on both the color and lightfastness of the dyes. In order to explore these effects more extensively, five different solvents were selected for our present tests. They reflect a range of properties with respect to dye solubility and volatility/evaporation rate. Among them are solvents commonly used in the conservation of art and artifacts, as well as some others used in previous testing by Ciba-Geigy. Unusually toxic solvents or solvents that present other problems precluding their general use in restoration work were excluded.

The solvents we are testing include:

  • Acetone
  • Ethyl acetate
  • Ethanol
  • Isopropanol
  • Propylene glycol monomethyl ether (PGME).
acetone_PGME

Dye sample Red BL (CIGN Solvent Red 122) purchased from Kremer. Note the difference the solvent choice makes in surface texture/coverage between the sample dissolved in acetone (left) and the same sample dissolved in PGME (right). AMNH/F. Ritchie

Dye concordance table

Concordance of dye materials by current and former product names, Colour Index Generic Names (CIGN), chemical composition, and source.

 

Accelerated Aging Chamber, Part 2

Troubleshooting

Conservation Intern, Associate Conservator, and Project Conservator working to troubleshoot an issue with the water purification system that occurred while this post was written. AMNH/F. Ritchie

Part 1 of our posts on accelerated aging instrumentation introduced the Q-SUN Xe-3 accelerated aging chamber. In this posting we describe some of the challenges we have experienced in installing and operating the machine; challenges which were unexpected and eye-opening. Problem-solving these situations has been such an important learning experience for us, demonstrating what taking on a project of this magnitude really entails.

Modifying the Lab

Our initial challenge was retrofitting the lab to accommodate the needs of the unit. In addition to electrical and plumbing adjustments to provide sufficient voltage, surge protection, purified water, and condensate drainage (all while retaining the ability to move the unit around the lab on its casters as needed), we had to install a ventilation hood over the machine with a fan and ductwork to vent its exhaust directly out of the building. This was necessary to limit the machine’s impact on the environment in the lab and adjacent offices, which otherwise became uncomfortably hot and cold respectively. The improved ventilation also allows the machine to cool itself much more efficiently, reducing both the noise and overall consumption of purified water – saving both our budget and our ears. We learned firsthand how important it is to moderate lab temperature when the HVAC system in the lab randomly failed and the machine was forced to stop because the chamber air rose to an unacceptable temperature. Luckily our maintenance staff provided the troubleshooting for this situation and the test cycle resumed within 24 hours.

Lesson: Make sure to understand completely the needs of a machine and its impact on day-today processes.

IMG_20151104_115246043

Ventilation hood and fan installed above the Q-SUN Xe 3 chamber to extract heat generated from the machine, helping maintain lab temperature. AMNH/F. Ritchie

IMG_20151104_115259244

New ductwork installed to direct exhaust from the Q-SUN out of the lab. AMNH/F. Ritchie

Setting Test Parameters

Our next unexpected hurdle was in setting our testing parameters inside the Q-SUN (i.e. the RH, chamber air temperature, and irradiance). Our previous dye testing was undertaken following the ASTM D4303 (Method C) testing standard in a chamber that did not have the capacity to control for RH. Because our Q-SUN Xe-3 chamber can be run with RH control, we initially chose a different standard ASTM D4303 (Method D). Immediately, to our horror, we found that condensation was forming inside of the machine, dripping onto the carefully prepared samples and making them unusable.

Initial troubleshooting with Q-Lab Corporation (the Q-SUN manufacturer) focused on possible problems with sensors or calibration within the machine, but that did not solve the condensation problem. Ultimately we learned that the D4303 test Method D is outside the capabilities of the Q-SUN Xe-3 (and apparently outside the capabilities of any humidity controlled xenon arc testing chamber). This was not an intuitive conclusion since Method D is specifically written for a Humidity Controlled Xenon Arc Device. As such, we have adjusted our test parameters so that they now lie well within the capabilities of the machine, and more closely replicate the Museum’s diorama conditions that we are chiefly concerned with.

Lesson: Understand that standards are often simply guidelines to follow to provide consistent parameters for comparison. Standards can (and often, should) be adapted to meet necessary requirements.

Dealing with Malfunctions

The most recent wrinkle in our operation of this machine was the spontaneous cracking of one of the UV-blocking filters that we are using for half of the testing rounds. Though this required us to suspend our testing for a few days, Q-Lab Corporation was very quick in providing a replacement, and since then we have been able to run the unit without incident.

cracked filter with arrow

Crack in a portion of the glass UV filter. AMNH/F. Ritchie

Lesson: Be flexible and ready to deal with unforeseen circumstances, and maintain a good relationship with the manufacturer of your equipment.

Budgeting for Consumables

The Q-SUN Xe-3 requires air filters, water purification filters, replacement lamps, sample preparation supplies, and many other expendable items that add cost beyond the initial purchase of the machine. Our grant budget has been adequate to deal with consumable materials, but we have realized that we must be prudent when running the machine and we must stay on top of ordering replacement supplies. There are even differences between test cycles. We are finding that our UV-filtered test cycles use up the lamps and water filters more quickly than the UV-rich test cycles.

Lesson: Pad your budget for expendable supplies and be sure to order the next set of replacements as soon as you install the first set.

IMG_20151104_115333353

Row of Q-SUN replacement lamps awaiting installation. AMNH/F. Ritchie

IMG_20150902_145310932_HDR

Project Conservator replacing a lamp. AMNH/J. Sybalsky

CONCLUSION

Owning and operating an accelerated aging chamber, at least one as complex as the Q-SUN Xe-3, is more than a plug-and-play operation. We hope that the steepest part of the learning curve is now behind us, but past experiences have taught us to expect that new issues will present themselves as we continue to work with this machine.

Lesson: When using any new tool or taking on any new experimental analysis, be sure to build time into the project timeline for troubleshooting.

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!