Giorgio Trumpy presented interesting work he has been conducting on the “virtual cleaning” of paintings at the National Gallery, Washington, D.C. as a post-doc with John Delaney. He described a mathematical/- computer model which is being developed to predict and represent what a painting would look like after the removal of a yellowed varnish. The idea is not to replace the conservator, but to provide a tool in helping conservators visualize the results of such a treatment.
The model makes use of the contribution of the scattering (diffuse reflectance) of light from the surface of a painting with and without an aged varnished, after application of a fresh varnish, and from the interface of the paint layer and the varnish surface itself. Measurements were made on two paintings to obtain values for use in the model, and the optics of the yellowed varnish itself was estimated by measuring the transmittance through a solvent containing the dissolved yellow varnish.
The results give a pretty good indication of what the painting might look like after removal of the vanish. Click on the image* to see the animated .gif (it worked on my computer). There are differences with the paintings however as can be seen comparing the virtual cleaning image and the after (real) cleaning image. Trumpy thinks that the differences are due, among others, to the fact that the model does not account for local variations in varnish thickness or aging, and the use of the transmittance values for the yellow varnish as measured through the solvent.
In a follow-up e-mail van John Delaney I understood that the goal of the work is to better understand which factors are important for this kind of modelling work, and also to determine the limits of what the model can do. Still, I found it fascinating to see how far they had gotten.
* Image courtesy of G. Trumpy and J. Delaney, Scientific Research Department, National Gallery of Art, Washington, D.C.; detail from “Flowers in an Urn” by Jan van Huysum, c. 1720/1722, oil on panel,
79.9 x 60 cm.
Christophe Vischi and Ariane Lalande presented a talk on practical tests they conducted to determine how to clean brass mats of photographs from the collection of the Colby Curtis Museum, Stanstead, Quebec. These mats suffered from multiple corroded spots (which I know as pitting corrosion from industry), containing stable Cu2O cuprite and active atacamite Cu2Cl(OH)3. They compared two electrochemical methods and the use of an ion exchange resin to treat the mats:
– spot electrolysis using an EDTA electrolyte and at 9 Volts,
– brushing an glycerine electrolyte on the object, wrapping it in aluminum foil and laying it a humid chamber
– use of the ion exchange resin, Amberlite IR 120 HM. This comes in the form of beads, which were applied locally on the object as a poultice using a fine brush.
The authors did not obtain good results with the electrochemical methods, with staining being a problem for the spot electrolysis, and a gray patina a result of the wrapping method. They chose the method using the ion exchange resin. It was found that grinding the beads before application improved the results. Very local cleaning was possible, and the solution could be rinsed off with a mixture of ethanol and water. Still, there were flecks left where the pitting corrosion was, but these could be retouched to match the finish. Care had to be taken to avoid staining uncorroded areas. The result appeared to be satisfactory, and they want to continue work on optimizing this method.
I would like to note that electrochemical methods should not be ruled out based on this paper. When performed properly, electrochemical cleaning can be used to clean most metals found in museums. C. Degrigny, among others, has demonstrated that local electrochemical cleaning can work under properly controlled conditions (cathodic potential/voltage), using the proper equipment, and electrolytes. The aluminum foil method might have worked if the objects were not wrapped (traps the reaction products), and the proper electrolyte was used. If I heard correctly, glycerin was used as the electrolyte, but it is non-conducting, so it could not have worked.
Dean Koga and Michael Schuller gave an interesting and useful talk on the protection of original Tiffany stained glass windows at the Congregation Shearith Israel in New York City during heavy renovation work there. The talk gave a clear outline of what they did and how others can prepare for such events. It should be noted that there was little warning between the time that the Congregation was informed of the work and the start of the work.
They carried out the following actions (which I would strongly recommend):
- Look for local engineering expertise in vibrations and the monitoring of vibrations. Michael Schuller represented this company.
- Look at existing (inter)national standards for the protection of buildings due to vibrations including those caused by construction work. These included building codes for New York City, international codes for France and Russia, and the vibration literature.
- Document fully any preexisting damage in the stained glass windows
- Look at the levels of current existing vibrations due to, for example, traffic, wind, opening and closing of the windows or doors. This showed that such events, as well as the opening and closing of the windows themselves were also a source of background vibration and shock.
- Determine limits for vibrations including a warning limit, and a limit where work has to immediately stop. These were 0.15 in/sec (3.75 mm/s) and 0.2 in/s (5 mm/s) for the low vibration frequencies expected.
- Negotiate with contractors to use more “gentle” construction methods. The contractors agreed to avoid using a wrecking ball for razing the old part of the synagogue, and to use augured piles for the foundation instead of pile driving.
The precautions were successful. No damage was found after demolition work, and only one new crack was found near an operable window. It was interesting to hear that wind pressure on the windows actually increased due to exterior protection. The authors were aware that the vibration sensor they used, a geophone actually designed for earthquake monitoring, was too heavy for the job, but time constraints limited their choices. A lightweight (several grams) sensor placed on the window frame or horizontal supports would have been better.
The authors recommended more studies on systems to protect stained glass windows, and testing to determine how much deformation/displacement such windows can tolerate. I would certainly agree with that.
“What is the value of conservation (of what I do)”, or, “What is the value for us, the funding agency, to (continue to) fund conservation (you)?”
One of the most important contemporary issues facing conservators today is the effect of the economic crisis and cost cutting on the preservation and conservation of cultural heritage. Conservators and other conservation professionals must continually defend their work and answer questions posed by funding agencies and sponsors, local, state, and national governments, the general public, and even many museums themselves. These include critical questions such as
– what is the value of cultural heritage in this day and age,
– how does one determine what is worth conserving, and
– why should cultural heritage be conserved, that is, why is conservation and why are conservators valuable?
In order to help answer these questions of “value”, the AIC organized the first of what hopefully will become a series of so-called Socratic dialogues at the most recent annual meeting in Indianapolis. At this first dialogue, forty participants and a number of observers investigated their own answers to the question, “What is the value of conservation (of what I do)”, or, asked from a different point of view, “What is the value for us, the funding agency, to (continue to) fund conservation (you)?”
A Socratic dialogue does not answer the question posed, but helps the participants dig deeper into the issue. The Socratic dialogue brought up a number of issues and concerns, not only referring to the question of what the value of conservation is, but also of what value itself means, what motivates conservators, and what it is that they are conserving. Here is a sample of what the participants found to be the essence of the dialogue:
- What is “value”?
- Are values shared across cultures? Across time?
- How has the value of the conservator changed over time?
- Can we combine our values with those of our stakeholders in our treatments?
- How do we preserve intangible aspects of cultural that do not have objects associated with them, i.e. … sense of humor?
- Positioning material culture with the richness of human engagement.
- If the value of conservation is that it preserves cultural heritage, how do we justify the value of cultural heritage?
- How do we share our passion?
- How do we balance our role as interpreters with our ideal of neutrality?
- Conservators contribute something essential to the significance of material objects and how these object can help us gain a better understanding of what it means to be human.
- Conservation is a tool that helps facilitate better understanding and appreciation of material culture through preservation and documentation.
- Value is intangible and conservators help to preserve often physical objects that give people the chance to connect, now or eventually, to those very personal values.
- ΔG = ΔH – TΔS
- I leave better able to articulate the societal importance of what we do and secure in the knowledge that others grapple with the same issues.
The response to the Socratic dialogue was overwhelmingly positive. The participants found this form of dialogue an excellent way to delve deeper into the question. It gave them the possibility to think and express their own opinions without being challenged, and then have a “safe”, non-aggressive environment to consider the deeper issues at hand. A full report has been submitted to AIC News for publication in September.
The AIC plans to conduct a Socratic dialogue at next year’s annual meeting in San Francisco. While a number of the essences are ideal topics in themselves, if you have suggestions for a topic, especially related to the sustainability theme of the meeting, please send them to the moderator/organizer, Bill Wei at firstname.lastname@example.org . For those participants who did not leave their e-mail addresses, he would also like to hear your comments and suggestions.