Jennifer McGlinchey Sexton, Conservator of Photographs at Paul Messier, LLC, presented on the testing of reference cards and the development of new imaging protocols that are so desperately needed in our field for increased standardization and comparability of photographs taken of UV-induced visible fluorescence phenomena. The project started by private photograph conservator Paul Messier in 2006, under the servicemark name UV Innovations (SM), was taken over by Jiuan-Jiuan Chen, Buffalo State’s Assistant Professor of Conservation Imaging, Technical Examination, and Documentation at Buffalo State College. Sexton has directed development of the Target-UV™ and UV-Grey™ products since 2012.
Many a visual examination is followed by technical imaging, including both Ultraviolet Fluorescence (UV-FL) and Visible-Induced Luminescence (VIL), and Sexton’s talk first reiterated why observing cultural material by using carefully selected wavelengths of light is important: It is non-invasive, relatively inexpensive, accessible, and (largely) commercially available. As a surface technique, UV-induced fluorescence probes outside layers, coatings, optical brighteners, mold, tidelines, and organic-glaze pigments above bulk pictorial films. Although it is a technique we rely on for the large majority of condition assessments and technical studies, our documentation remains unstandardized, and essentially, unscientific. With so much to gain by standardizing our capture and color-balancing process, as well as by taking careful notes on the equipment used, the prospect of the Target-UV™ and UV-Grey™ UV-Vis fluorescence standards is certainly an exciting one.
UV-FL images are unique in that they contain diagnostic color information, hence the need for standardization, which would enable cross-comparison between colleagues and between before- and after-treatment documentation. The beta testing of the UV target which was been carried out for 2 years has attempted to account for the most significant variables in the production of UV-FL images. The talk evidenced the enormous amount of collaboration and communication needed to streamline the significant aspects of equipment choice, the optimization of acquisition, and the documentation of post-processing methods. The goal was to increase reproducibility and comparability. Sexton’s presentation showed that the beta testing of the product achieved demonstrable results in terms of uniformity of output.
Development of the UV target was begun in collaboration with (Golden) to produce stable fluorogenic pigments of known color values and known neutral-gray values (which were evidently produced by mixing the red, green, and blue fluorogenic pigments). Neutral gray was defined as a gray which was interpreted as neutral by many viewers and which performed similarly under many different conditions. Including such color swatches within a photograph–for the purposes of color-balancing and correcting any variation in the Red-Green-Blue channels for each pixel–is a very familiar principle in visible photography.
A second consideration made for the round-robin testing was that of intensity, which is a variable somewhat unique to UV-FL photography. The nature of the emissive source must be noted for purposes of calibration and exposure, especially as all light sources currently used in fluorescent photography lack stability over long periods. The output of a lamp with fluctuate over time, and this makes relative intensities of materials illuminated with some lamp types very difficult to determine. Even when this particular factor is taken into account, other variables, such as the distance of the lamp to the subject and the wattage of the lamp will effect intensity. It is also possible that multiple emitting sources could be present. These factors should be included in the metadata for the exposure.
To control for this intensity factor, beta testers were to divide their sources, distance-to-subject, and wattage parameters into three different intensity levels which were best matched to certain analyses: “Ultra” was beta-tested for analysis of optical brighteners and other products produced specifically to fluoresce. “High” was best for the analysis of natural and thicker fluorescence, perhaps of a paint film such as zinc white, of some feathers (see Ellen Pearlstein’s talk from this year “ Ultraviolet Induced Visible Fluorescence and Chemical Analysis as Tools for Examining Featherwork”), and uranium glass colorants; and “Low” was used to image thin applications of resins, varnish, and sizing films.
A third variable was that of camera sensitivity, which varies with manufacturer (proprietary internal filtration and software), camera type (either DSLR or digital back cameras), as well as with sensor type (CCD or CMOS, modified or unmodified). Different filters were tested (Kodak Wratten 2e pale yellow filter, PECA 918, and an internal blue-green IR (BG-38) filter). These types of internal filtration are typical on digital cameras to block out IR and some red light to bring the camera output closer to the typical photopic curve of the eye and more closely mimic human vision. The 2e filters UV radiation and a small amount of the blue light commonly emitted by UV lamps, while the Peca 918 is used for IR blocking.
The fourth variable tested was the source type. Those tested included low-pressure mercury, high-pressure mercury, arc and metal halide arc lamps. Although LEDs were used at some institutions, many of these have a peak emission at 398 nm, which is barely in the ultraviolet range. Greg Smith at the IMA analyzed Inova X5 UV LED, and found that it does contain UV but is more expensive. Other products show a large difference in emission peaks which often cannot be accommodated by a simple white-balancing operation. Therefore, testing limited the peak emission to the most common types, emitting between 360 and 370 nm.
The last variables that were analyzed were those of post-processing procedures and software and of user perception and needs. An problematic paradigm identified over the testing period was that of the image being readable or resolvable vis-à-vis a particular argument versus the image being strictly accurate and well-calibrated. A photograph may accurately render the intensity of the fluorescence but it may be so completely underexposed so as to be unreadable.
Testing showed that, despite these difficulties of calibration and subjective experience, that the workflow incorporating the UV Innovations standard, showed a marked increase in standardization. Round-robin testing was completed by eight institutions in the US and Europe in May 2013. Fluorescent object sets were shipped along with the UV standard and filters. Each test site collected two image sets, one named “a,” using the lab’s current UV documentation protocol with color balance and exposure set “by eye,” and the other named “b” using the UV innovations protocol. The increased control provided by the use of the standard was evidenced by the average delta E of L*a*b* data points as well as the average standard deviation of RBG data points for both a and b sets as each institution. By way of example, the ‘Low—a” set showed an improvement from a delta E of 18.8 to the ‘Low—b” with a delta E of 4.9. The average standard deviation in-between these two sets showed an improvement from 32.8 to 6.2!
The presentation went into depth about how this data was collected, how variables were controlled for, and how the data was analyzed, and it showed convincingly that despite the high variability of current work flows, the UV Innovations UV-Grey card and Target-UV standards in conjunction with standardization of UV source and filtration can markedly improve the image variability of UV-FL photography.
One variable in “extra-spectral” imaging that was not addressed in this talk were the spatial inhomogeneities of the light source, or the gradient that results from the use of an inconsistent light source. This could be especially problematic if using UV-FL photography for condition imaging, and “flat-fielding” should be considered as a possible augmentation to the ideal image-acquisition protocol.
There is still further research to be done before this product hits the market. A fourth intensity level will be added to increase the flexibility of the product. The current prototype features two intensity levels on the front and two on the back. Notably, artificial aging must be done to determine when the product should be replaced. As this current standard only operates over UV-A and UV-B, UV Innovations looks forward to developing a UV-C standard, as well as a larger format target.
The prototype of the Target-UV and UV-Grey cards were handmade, but the company hopes to overcome the challenges of large-scale production and distribution by Fall 2014.
Category: Research and Technical Studies
Posts on research, materials & techniques used in and by conservators
42nd Annual Meeting – Research & Technical Studies Session, 29 May, "A Closer Look at Early Italian Panel Paintings Session: Imaging Cross-sectional Paint Samples from the Walters Art Museum" by Zachary Voras, Kristin de Ghetaldi, Tom Beebe Jr., Eric Gordon, Karen French, Pamela Betts, Glenn Gates
A problem encountered in the study of paintings is distinguishing the medium in which they were created, and delineating layers which may include different media of mixtures of media. This was the subject of a paper presented at the Research and Technical Studies session.
It is not easily possible to distinguish between oil paintings and tempera (egg-based) paintings by eye, or using many analytical methods. The authors discussed the benefits and drawbacks to three main types of analysis that are used within paintings conservation: cross-sectioning, Fourier-Transform Infrared (FTIR) spectroscopy, and thin layer chromatography (TLC). FTIR, for example, cannot distinguish between egg proteins and glue, and the results can be masked by pigments or colorants. None of these methods, as discussed, can be definitive when it comes to mixtures of media such as tempera grassa.
The author also considered the effectiveness of other common methods, such as GC/MS (Gas Chromatography – Mass Spectrometry). The main drawback to this is that results cannot be compared across different experiments if the methodology varies even slightly.
The combination of these drawbacks in common methodologies led the authors to pursue Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), a high-resolution technique that is better at separating and identifying fragments which are different but have similar masses. It also allows for the presence of specific compounds to be ‘mapped’, giving a helpful visual of layers and levels. Using this method, they were able to map for amino acids, identifying the presence of animal glue in a mixture. Practically, this was shown to differentiate between a gesso-size ground and the glue layer which was determined to have been purposefully added.
The talk concluded with a reminder that this technology, as with most, works best in conjunction with other methodologies. While this is an important point to remember, the potentials of this technique are exciting. I’m very interested to see the potential that this technique has for three-dimensional objects with multiple painted or gilded layers. I hope that someone pursues this, and that the technique is able to be harnessed across conservation disciplines.
42nd Annual Meeting- OSG + RATS Session, May 30, “Blue, Red, and Wound All Over: Evaluating Condition Changes and Cleaning of Glass Disease on Beads” by Robin O’Hern and Kelly McHugh
Glass disease, weeping glass, glass deterioration, funky glass* (*author’s description)–just a few of the many names used to describe the degradation of glass beads that museums have observed as a white precipitate/cloudy appearance and/or cracking and splitting. If you’ve observed this in your collection, take notice- Mellon Fellow in Objects Conservation, Robin O’Hern, is on the case.
O’Hern has taken advantage of the history of glass disease detection at the National Museum of the American Indian (NMAI) and begun evaluating how the different cleaning methods have fared over the years. In 1999, Kelly McHugh (research supervisor and co-author) and Scott Carrlee performed a condition survey of the NMAI collection. The collection was moved into a state-of-the-art storage facility after the survey, where the RH has remained constant, but at a higher level than recommended for glass pieces. (The beads are present on composite pieces with hide, bone, shell, feather, hair, etc. and therefore the environmental controls must address as many materials as possible, not just glass.) Some of the pieces were treated at that time, and others have been treated in the interim years. Using the museum database, O’Hern found that 25% of the condition records that list glass beads as a material also list glass disease. O’Hern has performed another survey, this time seeking to observe condition changes over the past 15 years in a selection of objects from the 1999 survey, to assess treatment technique (ie, which solvents worked best to reduce glass disease), and to discover susceptibility trends (which beads are the worst culprits).
To understand the beads, O’Hern provided background on history of use and manufacture.
- Glass beads arrived after contact with Europeans in 1492
- Pony beads were introduced after 1675
- Wound beads were introduced after the late 17th century
- Seed beads were introduced 1710-1840
- Red beads were colored from copper in the 17th century, ruby red in the early 18th century, and selenium in the 1890’s
- Blue beads were colored from copper or cobalt, but from 1640-1700, they were tin-rich
- Beads can be made by pulling the heated glass, called “drawn,” or by winding heated glass around a rod, called “wound”
- Glass is made from silica, alkali (to lower the melting point, but also makes it water soluble), and calcium carbonate (that turns to lime- it’s added to help stabilize the glass after the alkali)
There are several explanations for the cause of glass disease. Too little or too much of the lime (part of the bead’s composition) may cause water to leach out of the glass matrix as ions that then form salt on the surface of the bead. The environmental conditions, such as fluctuations in RH, or materials in proximity, such as semi-tanned hide, may accelerate glass disease. As seen from the list above, the beads were manufactured over a range of time, in different ways, and in different places.
As you can tell, there are many factors to research when evaluating glass disease. O’Hern addressed as many as possible while still managing the scope of the project.
Survey Results
Condition Change: By comparing condition of the beads today to past condition/treatment reports, 16% of the beads have more deterioration now than in 1999. Measuring pH was used in addition to visual examination to determine condition. Some beads that did not look bad had a higher pH (above 7), signaling glass disease. Some beads that looked hazy did not have a higher pH, meaning no glass disease (perhaps hazy from manufacture).
Differing Manufacturing Techniques: Wound beads have it worse than drawn beads–95% of wound beads have glass disease. This could be because they have a compositional percentage of lime that is less stable.
Differing Colors: Black, red, and blue are the most disease-ridden. O’Hern looked through the museum database and found that the entries with the most “glass disease” indicated had blue beads. Blue beads are very clearly the “winner” of the glass disease competition, followed by red and black.
Treatment Techniques: Here’s where it gets even more interesting. The conservation literature and posts on the Objects Specialty Group list serve debate the use of three solvents to remove the salts on glass disease: water alone, ethanol alone, and a 1:1 water:ethanol mix. By comparing the 1999 survey to her own results, O’Hern capitalized on real-time aging to observe how each solvent mixture fares over time. Water-cleaned beads had a 50% rate of glass disease return; water:ethanol-cleaned had a slightly higher than 50% rate of return; ethanol-cleaned had the least amount of return at just under 50%. However, when looking at the beads cleaned with ethanol over the same time period as those cleaned with 1:1 water:ethanol (removing the very oldest treatments), the rate of return for glass disease falls to 40%.
(Note: Acetone has also been listed as a solvent for cleaning glass beads, but since the NMAI doesn’t use acetone, it was not included in this research.)
Other Observations:
1. Measuring pH is essential because beads may look like they don’t have glass disease, but are actually more alkaline. Measuring pH is also quick and easy- cut your pH strip to a small piece, slightly dampen it in deionized water, press it onto the bead for 3 seconds, and then determine any color change in the strip.
2. The most affected beads were those sewn onto hide, but the disease was present when beads were in contact with many other materials as well.
3. Although cleaning with ethanol is a better choice for long-term disease prevention, the solvent chosen should still depend on the substrate around the bead.
Advice from O’Hern:
1. Record treatment materials when removing glass disease.
2. Take BT and AT details of beads so you can easily compare for condition changes in the future.
3. Measure the pH of the beads… and RECORD THE RESULTS.
4. Have consistent monitoring of glass disease.
As an audience member, it’s always exciting to see a project that has results, especially on a topic that is not studied as extensively as it persists. This is definitely a postprint worth visiting for more details and results.
For other examples (and some “good” photographic examples), visit Ellen Carrlee’s project “What’s that White Stuff?” that she and (then WUDPAC graduate intern) Christa Pack reported on in Ellen’s blog: http://alaskawhitestuffid.wordpress.com/2011/08/09/glass/
42nd Annual Meeting – Paintings Session, May 30, "Aspects of Painting Techniques in 'The Virgin and Child with Saint Anne' Attributed to Andrea Salai" – Sue Ann Chui and Alan Phenix.
This paper, presented by Sue Ann Chui, intrigued and enticed us to want more. She noted at the beginning that the title had changed to “Leonardo’s Obsession: A Workshop Variant of his ‘Virgin and Child with Saint Anne’ from the Hammer Museum, UCLA.” This is a pertinent point to keep in mind in the broader scope of the day’s PSG talks.
Leonardo da Vinci spent fifteen years working on the painting of “Virgin and Child with Saint Anne” (now at the Louvre), keeping it in his possession, leaving it unfinished at the time of his death. While continuing to work in his studio, other variants were being created in the workshop. It was noted that the Hammer painting is in remarkable condition (both structurally and aesthetically) and that the panel is virtually unaltered.
The oil on wood panel painting, in storage for many years and thought to be an early copy, was attributed to Salai (Gian Giacomo Caprotti da Oreno 1480-1524). The panel support, estimated to be poplar with coniferous wood battens, tangential cut and not thinned, is remarkably close to Leonardo’s original panel (the “Louvre” panel) with similar tool marks and dowels. In addition to these similarities, the panel’s thickness (2-2.8cm) would suggest that both wood panels came from the same workshop in northern Italy.
Analysis revealed the ground to be calcium sulfate and glue with an imprimatura of lead white. Compositional changes can be seen in the under drawing (infrared imaging) of Saint Anne’s left foot and several other areas. Walnut oil was characterized as the binding medium in other samples. Pigments were characterized as lead white, carbon black, vermillion, lead tin yellow, red iron oxides, natural ultramarine, azurite, orpiment, transparent glazes of copper green and red lake.
The Virgin’s mantle, with a complex stratigraphy, presents some interesting questions. Does the stratigraphy represent an original sequence or changes by the artist? Analysis of the blue mantle reveals three applications of grey, along with ultramarine, and two applications of red lake glazes on top of the imprimatura and below the grey layers. Is a thinly applied transparent glaze as a preliminary layer, similar to Leonardo’s technique, intentional? The purple toned sleeve of Saint Anne, comprised of reds, red lake and layers of what appear to be retouching varnish is changed from a red-brown to a purple color similar to color found in the Louvre painting.
Two interesting finds in the Hammer Museum’s panel were imprints from fabric and fingerprints. Historical references mention the use of a textile to even out a glaze, as seen in an area of blue on the panel and using the palm of the hand to uniformly spread a glaze (leaving fingerprints in the paint – who might those fingerprints belong to?). Differing paint application in the scene’s plant foliage hint the passages may be by two different hands. Fine brushstroke’s in the face of Saint Anne suggest a very accomplished artist, leaving us to wonder if perhaps the master provided some assistance to workshop apprentices. It would seem the Hammer panel was almost certainly created in da Vinci’s studio.
The change in the title of the presentation tied in nicely with Elise Effmann Clifford’s presentation “The Reconsideration of a Reattribution: Pierre-Edourd Baranowski by Amedeo Modigliani.” In her talk Elise pointed out the biases and prejudices we all carry and need to be aware of. The need to look at each work afresh, consider all the findings of technical analysis, provenance, along with curatorial knowledge and instinct must inform how we approach artworks, while being mindful of our own biases.
As for my personal bias regarding the analysis of the Hammer panel I must admit that, like many in the attentive audience, I was hoping for a surprise ending that announced the Hammer painting would, in fact, be declared to be by the hand of the master. The session was packed full of high quality technical analysis (including a peek into workshop practices) suggesting deeper questions and the paint geek’s favorite, paint cross-sections!
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Additional articles you may be interested in being cognizant of biases, the writer’s and your own!
LA Times article on Hammer St. Anne:
http://articles.latimes.com/2013/feb/05/entertainment/la-et-cm-leonardo-getty-20130206
Recent article in The Art Tribune mentions the Armand Hammer, UCLA panel:
http://www.thearttribune.com/Saint-Anne-Leonardo-Da-Vinci-s.html
Guardian article on over cleaning of panel:
http://www.theguardian.com/artanddesign/2011/dec/28/louvre-leonardo-overcleaned-art-experts
ArtWatch article:
http://artwatchuk.wordpress.com/tag/leonardos-virgin-and-child-with-st-anne/
Credit: via Tumblr from WTF Art History
42nd Annual Meeting, Textiles Session, May 29th: Analysis of Organic Dyes in Textiles by Direct Analysis in Real Time–Time-of-Flight Mass Spectrometry by Cathy Selvius-DeRoo, Ruth Ann Armitage
Direct Analysis in Real Time – Time of Flight Mass Spectrometry (DART-TOF) was shown to be a viable method of organic dye analysis in the presentation by Cathy Selvius-DeRoo. The beauty of the technique is that it requires only a small fiber sample, and no advanced preparation such as dye extraction, in order to get positive identification for a variety of dyes, both plant and insect based.
The project began with a grant to purchase the equipment. From there, various colorants were tested from a dye sample book, in order to develop the protocol. The sample was put in the ionizing gas airstream (helium) and heated to a temperature of 350 – 500 degrees. The result was fast and accurate identification of several dye classes, such as quinones, tannins and indigoids.
The presenter had a relaxed, personable style and shared some of her tips for success as well as lessons learned, including: better results were achieved with the higher temperature and with the addition of acid hydrolysis, which could be added just prior to putting the sample in the airstream using an eyedropper. The presenter confessed that flavonoids could be difficult to discern because the spectra are very similar for the various components.
After the method proved reliable, the technique was tested on textiles with undocumented dyes. The most satisfying was to substantiate family lore on a Civil War coat. The story was that a mother of a soldier dyed a Union issued coat to resemble a Confederate coat. Analysis revealed that the indigo was overdyed with Walnut (also referred to as Butternut). Cool.
Full disclosure – I signed up for blogging this talk because I’m a bit of a science junkie. I don’t always understand it, and in a small private practice, I certainly don’t have a Mass Spectrometer in the studio, but I appreciate knowing how to solve problems and who to go to for help.
42nd Annual Meeting – RATS Joint with Objects Session, May 30, “Technical Study and Conservation of the ‘Bat Wing Ship,’ Background, Challenges and Surprising Discoveries, Lauren Anne Horelick , Objects Conservator, Smithsonian National Air and Space Museum
The compelling object at the center of this paper is an experimental prototype of a Nazi German jet powered fighter aircraft discovered by the Allies at the end of World War II and brought to the United States for study. Designed by the Horten Brothers (Reimar and Walter), this craft with a steel structure, paper-thin plywood veneers, and no vertical tail is regarded as a design predecessor to the stealth bomber. The aircraft, a model Horten Ho 229 v3 (the third and final version of this particular airframe) was captured when it was near completion in the Gotha workshop http://airandspace.si.edu/collections/artifact.cfm?object=nasm_A19600324000 Charcoal was said to have been added to the construction adhesives to make the aircraft invisible to radar.
While always a favorite of air flight/military history buffs, this craft has never been exhibited and has been the subject of increased interest in recent years due to what the paper’s author describes as a “sensationalized” documentary entitiled “Hitler’s Stealth Fighter.” This video, available on YouTube, is replete with inaccuracies including the assertion that it is stored in a “secret government warehouse” when, in fact, its current home is the Smithsonian’s Paul E Garber Facility in Suitland, Maryland. However, it will soon be moved to another disclosed location – The Udvar-Hazy Center in Chantilly, Virginia where it will have its big reveal.
In preparation for this move, conservators at the Smithsonian NASM carried out a technical study to inform treatment protocol for the stabilization of the unstable and extensively delaminating veneers. They sought to characterize and identify the adhesives and other materials employed and, in particular, seek evidence for the presence (or apparent lack) of charcoal.
The aircraft is 55.4 feet wide with a tubular steel frame. The engine rests in the center of the craft and it is covered in a plywood skin. There is a clear canopy for the pilot. Due to complications of working on the object in its storage location, the decision was made to disassemble the damaged plywood portions to allow for treatment of the panels in the conservation lab. The composite materials that were examined and analyzed included the plywood board, structural supports and spacer blocks including the adhesives used to attach these portions to one another.
After a literature review of plywood available in Germany before WWII, reference materials were acquired for the potential materials. A sampling protocol was developed and the object and reference samples were examined under visual and Polarized Light Microscopy, FTIR, Raman, and for selected samples XRD was employed. (There may have been other methods employed that I missed in my notes– GC-MS and 3-D microscopy were mentioned in the abstract – sorry if I have omitted something significant.) The analysis was done in conjunction with the Museum Conservation Institute.
The analyses yielded some unexpected results as some of the wood sample results varied from those specified by the Horten Brothers (as reported in their interrogation). However the substitutions of European Beechwood/Scots Pine for the specified birch was not very surprising to the authors given the materials shortages at the end of WWII. The adhesives tested were identified as urea formaldehyde and phenol formaldehyde. Confirming the presence of charcoal in the black paint/adhesive layers proved elusive. The black particles were difficult to separate from the matrix. PLM examination did not support the charcoal identification and they were found to be amorphous with XRD. FTIR analysis pointed to the presence of cellulose, hemi cellulose and phenolics. This could mean oxidized or charred wood – or neither.
Plans for treatment do not include repainting damaged areas as the author mentioned a growing trend toward exhibition of aircraft in a less heavily restored state. Beech veneers will be employed in areas of loss but were unavailable in the United States in the <1mm thickness required so must be ordered from Germany. Because the urea formaldehyde has cross-linked with age and become insoluble, the conservators are not as concerned as they might have been about adding new materials when they choose an adhesive to stabilize the veneers.
Details and updates on this research project and the treatment are available on the on the National Air and Space Museum’s Airspace blog http://blog.nasm.si.edu/restoration/horten-h-ix-v3-bat-wing-ship-may-2014-update/ The Bat Wing Ship is poised to be a popular attraction when it goes on exhibit – I know my interest has been piqued by this interesting talk!
42nd Annual Meeting, RATS session, May 29th, “Free fatty acid profiles in water sensitive oil paints: a comparison of modern and 15th century oil paints,” presented by Joy Mazurek, Assistant Scientist, Getty Conservation Institute.
A standard method in many conservation science labs is the use of Meth-Prep II (a methanolic solution of trifluoromethylphenyl trimethyl ammonium hydroxide) for the transesterification of triglycerides to methyl esters and esterification of free fatty acids (FAs). However, this method gives you the total fatty acid content of the sample, including free fatty acids, their oxidation products, fatty acids bound in metal soaps, and intact triglycerides. If you want to assess the extent of hydrolysis of an oil paint film, which might be related to water sensitivity, you need to use another method. What Joy has chosen to do is to modify the Meth-Prep II solution to prevent transesterification. She takes 400 μL of Meth-Prep II, evaporates it at 50 oC under nitrogen to remove the methanol, rinses it with toluene, and then adds 500 μL of toluene and 100 μL of t-butanol. T-butanol does not permit transesterification, but the methylation of free alcohol groups can still occur. So a sample can be analyzed with this modified solution- only the free fatty acids and fatty acids in metal soaps (non-glycerides or NG) will be methylated, and thus only they will quantified by GC-MS. Then the same sample can be re-treated with the normal Meth-Prep II solution to determine the fatty acids in triglycerides.
As with any quantitative GC-MS method there are potential issues. The sample needs to be well homogenized to ensure extraction and reaction. The efficacy in methylation of fatty acids soaps is not known, and so those species may not react fully and be underrepresented in the chromatograms. She also sees partial evaporation of her internal reference when the sample is retreated with unmodified Meth-Prep II and so that must be accounted for.
With all of these caveats in mind, they began to look at reference paints, including Bellini tube paints and handmade paints in cold-pressed linseed oil. For the new handmade paints the fatty acid profiles of the NG and the total FAs look similar. But pigments do make a difference- for yellow ochre and red iron oxide paints, the NG accounted for 50-57% of the total FAs, but for malachite and lead white paints the NG fraction was much lower, approximately 12%. This might be due to the formation of metal soaps and poor extraction of fatty acids from those complexes.
For water sensitive Winsor and Newton oils she found 17-37% NGs, although the high levels of palmitate present in cadmium paints may indicate the addition of palmitate soaps. However, there was nothing obvious about the fatty acid profiles that seemed to relate to the water sensitivity. Likewise, a water sensitive cadmium paint in a 1961 Jack Youngerman painting, while also having elevated palmitate levels suggesting palmitate soap addition, had nothing else unusual about the binder. To address this issue cadmium yellow and a chrome yellow paint were mixed with linseed oil, applied onto canvas and glass and artificially aged. The resulting cadmium yellow paint film was very water sensitive, while the chrome yellow film was not. However, there was no major difference between the NG ratios of the two films, and so something else must be rendering the paint sensitive. Furthermore, that sensitivity is not related to the palmitate soaps found in the commercial paints. So there’s more work to be done to determine what is going on, but in the meantime beware cadmium paints!
She had the opportunity to analyze a sample from MOMA’s Water Lilies by Monet, which has a very water sensitive surface. The total FA content of the samples were very low, indicating a very medium poor paint, consistent with Monet’s working method of removing media from his paints. The NG content depended strongly on the sample location and pigments present. The pink-orange paint contained no stearate or palmitate, while other samples contained very high palmitate in the NG fraction. Again, the origin of these differences cannot be explained at this time- but might be due to soap formation and incomplete methylation.
Additional objects tested with this methodology included a variety of Italian paintings ranging from 1595-1758 in date, a Byzantine painting, a Fayum portrait, and a Jackson Pollock painting. The Italian paintings had higher NG fractions than was observed for the tube paints and modern paintings, 22-66% of the total fatty acids, but the NG fraction did not correlate with the age of the material- so extent of hydrolysis cannot be used to determine the age of an object. One possible explanation for this is that paintings this old have likely been cleaned several times and this may have impacted the amount of free fatty acids. The Byzantine painting had a higher NG content of 40-90% and the high palmitate and stearate amounts suggested the formation of metal soaps. Joy found that the modified Meth-Prep method simplified the analysis of beeswax and resulted in less overlapped and confusing chromatograms. In 19th century beeswax she found palmitate and stearate, but in a sample of unpigmented wax from a Roman tomb, she detected neither of those species, implying that they had all evaporated with time. However, in the pigmented Fayum portrait both species were seen, which might be due to the formation of metal soaps, which would help preserve those species, or to the modification of the wax- a contentious subject in the art history field. The white sample from the Pollock painting contained no fatty acids at all, so they evaporated the Meth-Prep solution and reanalyzed it using a method developed for proteins and determined that it was actually a casein paint.
So this seems to be a promising method, and one that could fit easily into a laboratories work flow. Obviously there is more work to be done- particularly on determining efficacy of extraction of fatty acids from soaps and trying to determine how certain pigments create water sensitive films without altering the fatty acid ratios…
42nd Annual Meeting, Objects and RATS joint session, May 30th, “Animation Cels: Conservation and Storage Issues,” presented by Kristen McCormick, Manager of Art Collections and Exhibitions, Walt Disney Animation Research Library.
“Darling, forever is a long, long time, and time has a way of changing things.”
—Big Mama, The Fox and the Hound.
Kristen chose that quote to begin her talk, and indeed it is true of all objects in cultural heritage institutions. Her particular institution, the Walt Disney Animation Research Library is home to over 60 million objects, including animation drawings, pencil story sketches, watercolors, maquettes, and animation cels, the latter of which make up approximately 10% of the collection. Animation cells are transparent sheets of material, usually celluloid (nitrocellulose), cellulose acetate, or polyester that have been inked on one side, and then painted with gum based media on the other. These materials, particularly cellulose nitrate and cellulose acetate, are highly prone to degradation, so the library partnered with the Getty Conservation Institute to investigate the material nature of the cels and determine if the environmental conditions in the library (62-65 oF, 50% RH) and the microclimate packaging used were sufficient to protect these objects.
Phase one of the project involved investigation of the material nature of the animation cels, addressing the questions: what is the base polymer of the cel, what plasticizers are present and in what quantity? They initially used a portable FTIR and non-destructively analyzed 200 cells dating from 1937-2003, and then chose 80 of those items to do more in-depth, microdestructive GC-MS analysis on. In their initial survey they found cellulose nitrate, cellulose diacetate, cellulose triacetate, and polyester as the base support material. Surprisingly, the material used for a single production would not necessarily be the same; it seemed that the artists used whatever was at hand. Due to the limits of the talk time, Kristen chose to focus on the acetate films for the rest of her talk.
The cellulose acetate cels were found to contain 11 different plasticizers, 6 different types in the diacetate and 5 in the triacetate. These included triphenyl phosphate and a variety of phthalates including dimethyl phthalate (DMP) and bis(2-methoxyethyl) phthalate (DMEP). The plasticizers accounted for 12-19% by weight of the diacetate films and 8-14% by weight of the triacetate films. The diacetate films had an acetyl content of 35-41%, while that of the triacetate films was 43-45%. They are not sure if the range is due to partial hydrolysis or variability in manufacturing. There was no correlation between acetyl content and production year. However, it did appear as if the older films might be a bit more yellow, but more work needs to be done to determine if this is a viable observation.
Phase two was assessing the environmental conditions, or as Kristen said quoting Mufasa from The Lion King, “Everything you see exists together in a delicate balance.” Since this portion was focusing on cellulose acetate cels, Kristen referenced Image Permanence Institute guide for the storage of acetate film (https://www.imagepermanenceinstitute.org/webfm_send/299) and pointed out that the library’s storage conditions were outside of the optimal range recommended by the IPI (50 oF or lower, 20-50% RH). However, the cels are composite materials and it is unknown how the gum based paints would react to lower temperatures and what kind of mechanical stresses might be induced by those conditions, so they feel that the chosen conditions are a good compromise. However, belief isn’t the same thing as actual data, so they performed a survey using AD strips, looking at four vaults and 8 different locations. The strips were assessed after 8 and 96 hours and only one location, next to the Bambi collection, was off-gassing acid. They are planning on investigating that collection further to zero in on the problem.
The library also stores and exhibits the cels in passé-partout packages that include a window mat, the cel (usually hinged with Japanese paper and methyl cellulose), matboard, and a sheet of Artsorb conditioned to 50% RH. They include a RH strip to be able to easily determine if the Artsorb is working. This was supposed to be best working practice but after an exhibition of cels at the Grand Palais, they noticed microcracks and paint delamination and became worried that the package was concentrating off-gassed materials and accelerating the decay of the cels. To try and determine what was happening they extracted gas from a sealed package and analyzed the entrapped air by GC-MS. No acetate (at least above 800 ppb) was detected, suggesting that hydrolysis of the cellulose acetate was not occurring. AD strips were also inserted into packages and no color change noted. Thus they decided that neither the package, nor the exhibition conditions was causing hydrolysis of the acetate groups. They did find adsorbed camphor in a package containing cellulose nitrate, so scavenging of plasticizers might be an issue. Thus, they think that their environmental conditions are generally good and that the passé-partout packages are not the issue. They are not sure what caused the observed deterioration; whether it was mechanical damage caused by temperature changes, vibration during shipping, etc. and are continuing to look into this. They are also planning to begin looking at the ink and paints to better understand the complete nature of the cels.
For more information on this project see the Getty Newsletter:
http://www.getty.edu/conservation/publications_resources/newsletters/29_1/animation.html
42nd Annual Meeting, Textiles Session, May 29th: A Case Study Using Multi-band and Hyperspectral Imaging for the Identification and Characterization of Materials on Archaeological Andean Painted Textiles by Rebecca Summerour and E. Keats Webb
The paper began by acknowledging a third author who was inadvertently left off the program and abstract booklet, but will appear as a third author in the TSG Postprints. The paper was presented by E. Keats Webb, the digital imaging specialist for the Conservation Institute at the Smithsonian. She showed how by combining a lower resolution spectral camera (Surface Optics Corp SOC710) with a modified DSLR with bandpass filters, the resulting images could be used to identify certain pigments on a painted textile. The project began with four textiles being described as plain weave with color (a limited color palette of browns and blue/blacks) delivered in a paste form without an organic binder, the color remaining on one side – this is important, keep this in the back of your thoughts as you continue, dear Reader!
I live in Silicon Valley, but I am not tech savvy. I am also several years out of school and realize that I my not have the vocabulary to give a precise recall of the methods and analysis described. Having said that, I feel I did learn about a (relatively) low cost technique that would be helpful in characterizing pigments on textiles. Essentially, the technique required several images to be taken at various bandwidths along the visible to near infra-red spectrum. Knowing the reflectance spectra for a given pigment allows the researcher to target the images for analysis. The targeted images are overlayed to get the difference which results in areas that appear to fluoresce for a positive identification.
It was found that indigo was readily identified, whether it was used alone or as a component of other colors. Reds and browns proved a bit more problematic. The success of this technique seems to have been that there was a small color palette, as well as the textiles in question were of known provenance, so they already had an idea of the pigments to look for. Also, the pigments were on one side and in good quantity. They did not achieve good results with dyes or small samples due to background noise interference. Though it was brought up in the question/answer portion that HPLC gives definitive “fingerprint” spectra for positive identification, the imaging technique presented does not require sample-taking (important to the National Museum of the American Indian) as well as allows for the entire textile to be mapped, keeping the pigment identification within context.
I could see this technique as a very useful first step in pigment identification or potentially in identifying areas of restoration and the pigments used. I look forward to reading the paper in the Postprints.
International Symposium -The Non-Invasive Analysis of Painted Surfaces: Scientific Impact and Conservation Practice
Smithsonian American Art Museum & National Portrait Gallery
McEvoy Auditorium | 8th and G Streets NW | Washington DC, 20001
February 20 – 21, 2014
This two-day international symposium will focus on recent advances in technology and instrumentation for the analysis of painted surfaces. You can download an announcement flyer here: Non-Invasive Analysis of Painted Surfaces Announcement
While non-destructive and micro-destructive analytical methods are often essential for the study and understanding of paintings, recent developments in portable and non-invasive instrumentation have led to growing interest in the applicability of techniques to the study of paintings. Further, as new instrumentation becomes commercially available and more affordable, conservators and scientists are able to use non-invasive techniques for monitoring and analysis in new ways.
A particular focus of the conference will be the interpretation of analytical results from portable instrumentation including colorimetry, imaging and X-ray fluorescence spectroscopy. The format of the conference will include papers and panel discussions.
Registration for this conference is required.
A schedule of speakers and registration instructions are listed under the current courses section on AIC’s site.
http://www.conservation-us.org/education/education/current-courses/non-invasive-analysis-of-painted-surfaces
Presented in partnership with the Lunder Conservation Center, ICOM-CC Paintings Working Group, ICOM-CC Scientific Research Working Group, and FAIC.
Image: Smithsonian American Art Museum’s Chief Conservator, Tiarna Doherty, studies x-radiographs of Constantino Brumidi’s study for the Rotunda of the Capitol Building. (Photography by Conor Doherty)