Volume 12, Number 3, Sept 1990, pp.17-21
Three conferences are reviewed in this column:
11-29 June 1990, Getty Conservation Institute
This 3-week course was the first of its kind to focus on a problem common in ethnographic collections: powdering and flaking of paints and other coatings which contain little or no binder. Objects with this condition are difficult to handle and transport, and treatment is often necessary to save what little paint remains. Past treatments have been of limited success because consolidants tend to darken, stain, or disturb the surface.
Rather than providing definite answers, the course was a forum at which participants and instructors gave a new and broader definition to this difficult problem; the course acted as a starting point for finding innovative solutions. The participants generated many questions for future research, and it is hoped that other courses on the same topic will grow from this seed.
The course, which was the brainchild of Sue Walston (formerly of the Australian Museum), was taught by over a dozen instructors: a balance of GCI scientific staff and invited speakers. The first week focused on examination and documentation of the objects. In the second week, causes of deterioration, properties of consolidants, and treatment options were covered. During the final week, practical work was carried out on object facsimiles and treatment techniques were tried out and evaluated.
Practical sessions and exercises were carried out by 4- to 5- member teams. Each group had a distinct approach to the problems and emphasized different aspects. The groups presented their work during the final week, and the different perspectives enriched the learning experience.
Identification of surface coatings and paint media on ethnographic objects is difficult: few technical studies have been done, and the ethnographic literature is incomplete and sometimes unreliable. The coatings are often complex, multilayered structures including substances that are not paint pigments: clays, camwood, plant juices, oils, and blood are some of the kinds of coatings that may have been applied during manufacture or later use.
The examination section of the course focused on easy-to-use, low-tech methods: visual and stereomicroscopic examination, polarized light microscopy for identification of pigments, and microchemical tests to identify binding media. Dusan Stulik and the GCI Analytical Section developed a test kit for the identification of broad classes of natural binding media: oils, animal glue, egg, casein, blood, starch, sugar, and gums. The microchemical tests in the kit use a flow chart format, require little special equipment, and are based on medical research tests using reagents that are readily available worldwide. The GCI plans to publish these tests. During the course, interest was also generated in the development of a reference library for IR spectra for binding media used on ethnographic objects, similar to a project the GCI Analytical Sect. is currently working on for fine arts binding media. Lesley Bone at the deYoung Museum is looking into the feasibility and format of the project and will act as project coordinator.
The documentation section emphasized the development of clear, consistent, and comprehensive ways of recording information. John Perkins, former project manager for the Conservation Information Network, presented a session on information management. The need for a standard terminology became quickly apparent when it was shown that the 21 conservators who participated in the course described the condition of the same artifact 21 different ways. The importance of recording our thought processes during development of a treatment plan was also brought up. What is the prognosis for the object? What results do we expect from a particular treatment? Why are we doing something a particular way? These thoughts should be written down in the final report. A workshop on technical photography was taught by Tom Moon, former conservation photographer at the Getty Museum. Standardized photography procedures were suggested to allow meaningful comparisons between before and after shots.
The instructors for the sessions were Stefan Michalski, Senior Conservation Scientist for environment and deterioration research, Canadian Conservation Institute, and Eric Hansen, an Associate Scientist at the GCI specializing in organic chemistry.
Stefan began with a summary of paint deterioration problems and possible treatments. Coating/substrate systems were discussed in terms of their mechanical properties and stress/strain relationships, based on his research with gessos made from powdery fillers with very little binder. He emphasized that paint films have much less elasticity than an organic substrate on which they have been applied, and no consolidant introduced in a conservation treatment can counteract substrate movement during radical changes in RH. Stiffness of the paint film, which can lead to failure (flaking and cracking), will increase with low humidity, low temperature, physical aging (increased stiffness over time), and solvent leaching during cleaning.
Eric Hansen covered the properties of resins and solutions. He pointed out that increased brittleness of resins over time is not always due to crosslinking. Physical aging, the gradual continuation of glass formation at temperatures below the glass transition, also causes brittleness. Heating the material to Tg (glass transition temperature) can erase physical aging, a principle which is useful in treating brittle paint flakes. Pretreatment of an artifact with solvents before consolidation can also reverse physical aging and increase the solubility of a coating. Eric discussed the results of research undertaken at the GCI that have shown that solvent quality determines both working properties of a resin solution and mechanical properties of the dried film. Solvent quality is a measure of how well a solvent dissolves and penetrates a resin. This research also had been presented at the 1989 AIC meeting in Cincinnati.
In preparation for the course, Eric, assisted by Eileen Sadoff and Rosa Lowinger, had carried out research on the conservation of ethnographic painted surfaces, their work including a literature survey, a questionnaire sent out to objects conservators, and a study of techniques for making artificially aged object facsimiles to use for research and testing. [See Feature Article in this issue: "Investigations into Techniques for the Consolidation of High Pigment Volume Concentration Paint at the Getty Conservation Institute," by Eric F. Hansen and Rosa Lowinger].
One of the most important concepts introduced in the scientific section was "pigment volume concentration" (PVC). In industrial paint formulation, the "critical pigment volume concentration" (CPVC) is when the ratio of pigment to binder is such that all the voids between the pigment particles are just filled. The result is a coherent, glossy paint layer. This pigment concentration is typically between 50% and 85% (or 15-50% binder). Porous, matte paints found on ethnographic objects have greater than 90-95% PVC (less than 10% binder). Some materials used on ethnographic objects, such as chalk and kaolin, act as paints--opaque layers--only because so little binder is used. They have poor hiding power and become transparent when a lot of binder is added. Clay pigments such as kaolin and ochres adsorb water on the surfaces of their grains. They can be mixed with water with no binder at all, and hydrogen bonds between molecules of adsorbed water on the surface of grains will allow the coating to have some cohesion when dry.
In consolidation, very little consolidant is needed to hold the pigment particles together. If too much is added, a low PVC paint with a glossy surface and dark, saturated colors is produced. To maintain the original matte appearance and to avoid darkening, staining and gloss, one should start a consolidation treatment with a 0.5-1% solution and work up. The refractive index of the consolidant, and even the type of resin used (given complete penetration), should have little effect on the final appearance because so little binder is present. Since a consolidant introduced into powdery paint is essentially nonremovable, reversibility is not a critical issue; however, aging and color retention properties must be excellent. The use of thermosetting resins such as epoxies and diisocyanates, which have high strength in very low concentrations, was suggested by Eric as an avenue for research. A chemically bonded resin may provide good consolidation at a much lower concentration than a thermoplastic resin. The GCI is currently looking into the use of diisocyanates for the consolidation of adobe.
Complete penetration of the paint layer is another important factor in successful consolidation. The use of a late gelling resin, a low volatility solvent, or improving wetting by use of a surfactant all increase penetration. The aim is to get maximum movement and spreading of the resin into the paint film before it gels. Penetration can also be increased by consolidating the object in an atmosphere saturated with the solvent used to dissolve the resin.
In the final section of the course, practical work was carried out on artificially aged object facsimiles. The facsimiles were prepared using wooden blocks and palm spathes coated with kaolin, ochre pigments, Rickett's laundry bluing (which contains ultramarine blue and is used as paint in some places) and carbon blacks, mixed with very small amounts of various binders or no binder at all. The facsimiles were heated in an oven to accelerate flaking and delamination. The facsimiles were very useful for practicing treatment techniques. They eliminated the variables and unknowns found in actual ethnographic artifacts, and provided expendable materials for experimentation. On ethnographic objects needing treatment, a detailed study of the specific condition and materials present would be done, and careful testing before treatment, carried out on the actual artifact, would be necessary.
Treating the facsimiles with consolidation resins gave participants an opportunity to synthesize and experiment with the theories presented in the first part of the course. It became apparent that the method of application is critical to achieving visually satisfactory results. Appearance changes can be due to a number of factors: solvent reaction with soluble components in the surface coating, localized concentrations of resin, filling the voids of a high PVC paint with resin, or displacement of pigment particles. Techniques varied depending on whether the paint was flaking or powdery. Control of consolidant application and staining was found to be easier when dealing with flakes than with powdery paint; however, the flakes were often brittle. Treatment of the original binder with heat or solvents reverses the effects of physical aging and may leave the flakes less brittle. This method has the advantage of not adding new material to the paint, but often there is not enough original binder present to reactivate. As an alternative to reactivation of original binder, consolidation resins were applied under flakes either in solution or as a dried film that was later softened by solvents or heat to make it adhere.
For powdery paint, participants attempted to improve control over application of the consolidant and increase penetration. Two new techniques were introduced for experimentation. Stefan Michalski modified an ultrasonic humidifier to produce a fine mist of 0.5- 1% gelatin solution. This offered a much gentler method of application than a paint sprayer, and it eliminated the problems of rapid solvent evaporation that occur during spraying. The motorized base of the humidifier was filled with water, and a small plastic container of solution was placed on top. The container had a large outlet tube with a nozzle to deliver the mist generated. A small inlet line from a compressor pressurized the system and forced the mist out. The nozzle was designed so that a hose from a wet/dry vacuum could be attached to collect the overspray. The strange looking apparatus, affectionately called Michalski's Mister or Mr. Mister, performed well with organic solvents such as acetone and weak gelatin solutions. A mist could not be generated with solvent solutions of Acryloid B72; the polymer molecules were apparently too large and heavy to be suspended in the mist.
A second technique, proposed by Eric Hansen, involved consolidation of an object inside an "Atmosbag" (Aldrich Chemical Co.). The Atmosbag is a clear plastic glove bag that allows manipulation of the object in a solvent-saturated atmosphere. A container of the same solvent in which the consolidant is dissolved in placed in the bag with the object and all tools needed. After the bag becomes saturated with solvent vapor, the object is consolidated. The presence of the surrounding vapor allows maximum penetration of the solution into the coating, and gelling of the resin is prevented until the object is removed from the bag.
One of the extra benefits of the course was the bringing together of a worldwide group of ethnographic conservators to share their varied experiences and learn from one another. Twenty-one professional conservators responsible for the care of ethnographic collections participated, including WAAC members Sharon Blank, Lesley Bone, Robin Chamberlin, and Nancy Odegaard. Also participating were Rogelio Aquino, National Museum, Philippines; Gertrude Blasum, Hamburgisches Museum fur Volkerkunde, West Germany; Jeanne Brako, private conservator, Denver; Natalie Firnhaber, Anthropology Conservation Lab, Smithsonian Institution; Joan Gardner, The Carnegie Museum of Natural History; Susanna Gatenby, Australian Museum; Julia Gresson, Auckland Institute and Museum, New Zealand; Suzanne Hargrove, St. Louis Art Museum; Charles Hett, Canadian Museum of Civilization; Kulpanthada Janposri, National Museums, Thailand; David Lee, British Museum; Lisa Mibach, private conservator, Oberlin; Catherine Millikan, Museums and Art Galleries of the Northern Territory, Australia; Emmanuel Mmbando, National Museums of Tanzania; William Phippen, Peabody Museum of Salem; Toby Raphael, Harpers Ferry Center, National Park Service; and James Ssebadduka, Uganda Museum.reviewed by: Robin Chamberlin
A One-day Course held 6 April 1990 in Manchester, England
This excellent course was organized by Dr. Norman Allen & Dr. Michele Edge from the Centre for Archival Polymeric Materials at the Manchester Polytechnic. Although the organizers are not conservators or conservation scientists, and the conservatism of the approach taken in the field of conservation is quite new to them, the course was well arranged and useful.
Dr. Edge presented: "Fundamental Aspects of Polymer Stability: Long-Term Aging of Polymer Material." Her well-organized overview covered polymer characterization; the fundamental aspects of polymer stability based on structure, additives, and impurities; & polymer degradation and the resulting property changes.
Dr. Norman Allen presented: "Fundamental Aspects of Polymer Stabilisation." Dr. Allen's talk focused on polymer antioxidants and stabilizers that retard degradation by protecting against UV radiation and thermal effects, and he supplied the audience with a 47-page handout that detailed this information. The talk and handout contained many charts of chemical reactions, artificial aging data, and included specific antioxidants and stabilizers as well as concentration ranges for their use.
Velson Horie, the Head of Conservation, the Manchester Museum, University of Manchester, presented the third paper: "The Stability of Biopolymers" (skin, leather, feathers, and hair). Mr. Horie discussed environmental factors that accelerate the degradation of biopolymers, and he also raised the point that DNA from an historic figure may be present in clothing, which can provide important genetic information. This DNA is easily lost by washing.
Dr. J. S. Crighton of the Textile Department from the University of Leeds presented: "Textiles in Conservation." Dr. Crighton's paper focused on proteinaceous polymers found in textiles, including an organized view of the chemical structure of proteinaceous polymers as well as the chemical changes that they undergo when aging and degrading. He also suggested that it may be possible to shield fibres from UV radiation with a UV absorbing surface finish.
Velson Horie also presented "Coatings in Conservation," focusing on the negative effects of coatings used by conservators. He gave various examples of problem coatings, but the most forceful point he raised concerned the use of waxes. Waxes are insoluble at room temperature, virtually non-reversible, and often prevent further treatments, especially those involving adhesion. Furthermore, the polyethylene chains in synthetic waxes apparently chemically react and bond with copper-containing materials; in order to remove the bonded wax, physical disruption of the surface may be required. However, Mr. Horie pointed out that the environmental protection provided by wax coatings on copper-containing outdoor bronzes far outweighs these negative aspects.
Dr. Priest of the Paper Science Department, University of Manchester, presented an extremely lively and excellent talk: "Paper and Conservation." He began by explaining that paper and plastics are designed products, implying that they can be designed to last. His talk covered the composition of paper and the factors affecting its strength. The importance of sizing in paper and its impact on longevity was also covered. He also discussed four mass-treatment methods for dealing with embrittled paper in bound volumes: diethyl zinc; a process to introduce into books acrylic monomers which are later polymerized; a product requiring immersion called "Wei T'o;" and the Lithco process from the FMC Corp., which claims to deacidify and provide strength with a complex organic base dissolved in an inert, nonaqueous solvent Dr. Priest pointed out that neutral paper sizing methods are increasingly being used for economic reasons; this suggests that the problems of paper degradation may be reduced in the future.
The final talk was "Conservation in Information Storage Materials." Dr. Edge presented her recent work for stabilizing and prolonging the life of cellulose triacetate motion picture films. She uses a "tris" combination of three stabilizers in an aqueous solution which is applied by immersion. It works synergistically to scavenge acids, peroxides, and metal ions that are found in degraded film stock. The solution is composed of a metal deactivator to negate the effects of metal ion induced breakdown and to function as a primary antioxidant; a phosphinate to nullify the effects of peroxides, thereby inhibiting oxidative breakdown; and a hindered amine to act as a weak base to neutralise acid decomposition products and to act as a radical scavenger. Based on her artificial aging tests, the life of new cellulose triacetate film was increased from 35 to 215 years. This aqueous procedure is difficult to utilize with film images bound in gelatine, however. Also discussed: how metal containers catalyse reactions that degrade film stock, and the possibility of transferring film images to more stable film supports such as polyester.
I would like to thank The Conservation Unit for providing half of my course and travel fees.reviewed by: Don Sale,
4th Annual LAPNET Workshop--July 23, 1990
One hundred and forty participants attended the fourth LAPNet (Los Angeles Preservation Network) Workshop at Occidental College on July 23. Joanne Page was the chairwoman for the event.
The morning session began with Debbie Hess Norris discussing"Long Term Preservation Planning." She covered establishing the proper environmental and storage conditions, exhibition techniques, identifying the various photographic processes, and the conservation considerations involved in the various processes. Debbie had a very enthusiastic audience: they all commented on her depth of knowledge, her extensive collection of slides, and her wonderfully relaxed, informal style of delivery.
Following a lunch break, Carolyn Kozo, who is in charge of the Security Pacific National Bank Photograph Coll. at the L.A. Public Library, spoke about the 1986 fire at the library and their problems and recovery efforts in terms of the photograph collection.
James Evans, assistant photo conservator at the J. Paul Getty Museum, had been scheduled to be the next speaker, and everyone involved expressed their sadness at his death.
Debbie Hess Norris spoke about conservation treatment of deteriorated photographic print materials during the afternoon session.
The last presentation was given by Craig Klyver, Interim Library Director of the Braun Research Library at the Southwest Museum, and Alan Liechty, photographer.
They discussed the recent project at the Southwest Museum, in which the images in the photo collection were transferred to computer accessed laser video disc. They brought equipment along so the audience could see the video disc in action.
James Corwin, conservator at the Huntington Library, assembled a display of photographs representing the various photographic processes in use during the l9th and 20th centuries. He also helped all of the participants to make their own sunprints to take home as a souvenir of the day. In addition, he had secured catalogs from some of the suppliers of archival materials as handouts for everyone.
The audience response was very favorable; all seemed to feel it was an interesting day.reviewed by: Joanne Page
Timestamp: Thursday, 11-Dec-2008 13:02:29 PST
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