Volume 16, Number 1, Jan 1994, pp.28-30
Three reviews are included in this column:
The Gerry Hedley Memorial Forum on "The Mechanical Behavior of Paintings: Experience and Theory", was held in Ottawa at the National Gallery of Canada on October 22-23, 1993. Over a hundred participants attended the conference which featured fourteen speakers.
Talks ranged from overviews of structural treatments from the past twenty years to reports on current research. The speakers included Marion Barclay, Al Albano, Lucy Belloli, Paul Schwartzbaum, Wendy Baker, Debra Daly Hartin, Laszlo Cser, Timothy Vitale, Jim Coddington, Sandy Estabrook, Scott Haskins, Stefan Michalski, Rona MacBeth, Jean Francois Hulot and Alain Roche.
The format of the meeting encouraged open discussion during chaired sessions both days. Several talks focused on lining treatments. Marion Barclay reviewed the history of linings performed at the National Gallery of Canada and assessed their current conditions. Al Albano discussed his work in developing lining alternatives in the 1980's and evaluated those and other methods. Lucy Belloli and Paul Schwartzbaum both discussed the history of Fieux linings performed at the Metropolitan Museum and in the Peggy Guggenheim Collection in the late 70's and early 80's. The success of the treatments has been mixed: while Belloli reported that almost half of the Fieux linings at the Met have failed, Schwartzbaum found that nine out of ten of the Guggenheim linings have remained stable. Environmental conditions, failure of the silicone adhesive, as well as the technical methods of applying the linings were all cited as factors affecting the stability of these treatments. Wendy Baker described the use of a laser scanning technique to monitor subtle changes in a paint surface during humidification. The technique was used to study two previously lined portraits in the course of a humidification treatment. Debra Daly Hartin gave a report on the current phase of her study of lining systems based on peel tests. She previously talked on the subject at the September ICOM conference in Washington D. C.
There was also discussion on constant tension stretchers. Laszlo Cser described a new constant tension stretcher design he has developed in collaboration with Gustav Berger. The stretcher is made of extruded aluminum, with springs on the vertical side members. The merits and hazards of constant tension devices were debated by several conservators in a question and answer session after the talk.
Jim Coddington provided an overview of the development of suction tables and noted the important pioneering contributions made by several individuals and credited work being done today by Stefan Michalski and Marion Mecklenberg. Studies by both Michalski and Mecklenberg appear in "Art in Transit", published by the National Gallery of Art, Washington.
Several talks were presented on topics related to humidification of paintings. Timothy Vitale presented a model showing how conservators often empirically choose parameters for performing humidification treatments which reflect principles that can be demonstrated experimentally and generally fall within lower ranges of heat and humidity and length of exposure. Vitale noted that within these lower ranges, many practitioners are manipulating the glue layer alone. He also suggested that prolonged contact with water vapor may allow lower heat to be used for softening paint. Vitale noted that the rate of vapor loss from paint at elevated temperatures should be studied further. Sandy Estabrook gave several examples of typical humidification treatments she had performed in her private practice using a modified hot table and described some particular techniques she had developed. Scott Haskins also described typical humidification methods he has developed in the last ten years and shared tips on useful materials and products. Stefan Michalski presented an experimental model for determining the deformation of a paint film as a function of external force. Michalski demonstrated that temperature, humidity and time may be proportionally related and he constructed a graphical model to show how they may be varied to achieve predictable results. Rona MacBeth presented a report on her continuing research on the moisture absorption of paint films. MacBeth cited Gerry Hedley's work at CCI in 1985 and a paper she presented at the ICOM Dresden conference in 1990. She has found that there is a major differential in moisture absorption among pigments and that pigment size and layer structure contribute to this differential. Jean Francois Hulot and Alain Roche discussed their current study of the biaxial affects of humidity on canvas with respect to glue-lined paintings. They have found that tension in a humidified canvas is greatest in the weft direction, due to the crimp of the yarn. Several prepared samples of natural and synthetic adhesives were also tested using a tensiometer. Results indicated that natural glues can be 50-80 times more reactive than many synthetic adhesives.
Funds raised by the forum were donated to the Gerry Hedley Research Fellowship Endowment Fund at the Courtauld Institute of Art. The endowment will be used to fund post-graduate fellowship research.Reviewer:
5-9 July 1993
International Academic Program
Institute of Archaeology, London
This one week course consisted of both formal classroom lectures and practical labs for the purpose of gaining a better understanding of the properties of conservation materials and applying that information to treatment decisions. The course is part of the yearly summer school offerings at the International Academic Program organized by James Black. Velson Horie, Head of Conservation at the Manchester Museum, and Joyce Townsend of the Tate Gallery's Conservation Department were the primary instructors with additional guest lecturers providing more focused information. As this week encompassed quite an immense amount of material, this conference review attempts to present the basic structure of the course, an outline of the contents covered.
Overall the course was extremely well organized and well presented, allowing the participants to indulge in a week emphasizing conservation materials, their properties, and their application. Each day was structured with six hours of lecture and two hours of lab "practical". Bound lecture notes edited by C. Velson Horie were most welcome as they provide an organized reference for the future. His book, Materials in Conservation (Butterworths, 1987), has formed a starting point for the course and continues to serve as an excellent reference.
Though the course was open to ten participants from all levels within the conservation field, with this year's class including individuals from student level to senior conservators, it was assumed that all had a basic understanding of chemistry upon which to build. The course emphasis was on polymer chemistry, demonstrating how structure affects material properties and related functions. Observable properties of materials as experienced by the participants in the laboratory included mechanical properties such as film hardness and tensile abilities; setting properties with a focus on film spreading, shrinkage, and minimum film formation temperature; solvent properties with an introduction to solubilities by ASTM D3132, removability of materials by swab, and solution viscosity; the measurement of refractive index using the Rayner Refractometer; spectrophotometry using transmission spectra to detect shifts in films over time; and observation of the change in reflection that can occur upon consolidation. The labs were undertaken in groups of two with each lab group required to discuss a practical treatment problem and appropriate solution at the conclusion of the week.
Velson Horie began the course by introducing polymers, solvents, and related hazards in lecture format. Included was a discussion of the factors considered when choosing materials for a treatment. Not only are the applied conservation materials and the material forming the object being treated to be considered, but also any possible interactions between these materials. Covered were basic setting methods and levels of reversibility, followed by what a polymer is, the various properties and how these affect working properties such as application. Solvents used for applying and removing polymers were introduced. Considerable time was given to the criteria for choosing a solvent, including such considerations as chemical type, toxicity, flammability, viscosity, reactivity with the object, color, refractive index, etc. As their properties can be better understood by examining their chemical structure, a lengthy discussion of this led into solvent interaction with polymers. Dispersion, polar, and hydrogen bonding forces, as well as a three component system plotting these forces, the Teas Diagram, were discussed.
Lectures on polymers were continued throughout the week, focusing on the more commonly used polymers at length. Included were the vinyl-based, the acrylics, and the epoxies, with information presented on base monomers, initiators, possible stabilizers, application and deterioration. Lectures also included the emulsified forms of polymers, as these can give improved working properties. It was noted, however, that emulsifying agents and initiators can be unstable, contributing to a more rapid rate of deterioration.
Material was presented on cross-linking compounds which can be commonly encountered in both fine art materials and conservation materials. Polyester resins, phenol formaldehyde resins (bakelite), drying oils, epoxy-resins and polyurethanes were included. Though it is impossible to delve into any depth with such a broad subject, several generalities can be made. Horie's approach to treatment would include always choosing (1) the most stable material for any treatment, even if it is only "temporary", and (2) the simplest compound capable of accomplishing the treatment, as this reduces the complexity of the combined chemistry of the object and the applied material.
Topics presented throughout the week by Joyce Townsend included color measurement and coloring agents, refractive index, epoxy formulation and use, and painting varnishes. Color measurement allows one to objectively measure color shifts that can occur in applied conservation materials. The 1976 CIELAB System was felt to be of most use to conservation. Her information on refractive index included a basic introduction to that property with added information from her very recent and soon to be published research regarding refractive index of fine art material and conservation materials. Additional speakers included Tom Collins and polymers for papers, Yvonne Shashoua's material on mechanical testing, Philip Bale of Aqualon UK with a presentation on water-soluble cellulosics, and Eric Miller of the British Museum on stone conservation materials.
Joyce Townsend organized a class visit to the conservation labs at the Tate Gallery where treatments of painting, paper, and objects were discussed. This discussion, in addition those on treatment presented by each lab group at the end of the course, served well to bring the theory and understanding of materials into the realm of conservation practice.Reviewer: Shelley A. Svoboda
29 June 1993
Tate Gallery, London
The Turner Bequest to the Tate Gallery has provided the tremendous body of paintings, water-colors, and sketch books that forms the central focus of this day-long series of presentations. Included were not only discussions of investigations regarding Turner's materials and techniques, but also setting this information into the context of the 19th century.
The first presentation involved the research carried out by Joyce Townsend (Tate Gallery). This has been put into published form in the excellent book, Turner's Painting Techniques (Tate Gallery Publication, 1993), that accompanied the most informative exhibition of the same name running concurrently with the symposium. In her presentation, Townsend states that within the body of 19th-century paintings, condition problems stemming from artist's materials and techniques are not uncommon. With the works of Turner, however, condition problems are even more commonly encountered and sensitivity to treatment is often extremely pronounced. Townsend discussed absorbent and sometimes egg-based primings, pure oil layered with modified oil, the use of thixotropic paint, and varnish preference. Compounds found to have been added to modify his oils include waxes, natural resins, and bituminous materials. As bitumen can darken on heating, any treatment involving heat should be considered very carefully. Waxes could also, of course, be affected by heat. The presence of these three compounds in the paintings by Turner explain their great solvent and heat sensitivity. It should be noted that the presence of these modifiers was not a rare occurrence. Also contributing to the complexity of treating these paintings was the artist's rapid working technique, as this yielded variations in solubilities from area to area. While his finished works were most often varnished, it is not likely that his sketches would have been. An in depth discussion of these aspects of Turner's work and some of the treatment complexities that can be encountered are presented in Townsend's Turner's Painting Techniques.
Dealing more with the "context" portion of the day was the presentation by Leslie Carlyle (Canadian Conservation Institute), "Varnish Preparation and Practice 1750-1850". This lecture combined her earlier research involving artist's painting instruction manuals and the treatises on the arts, (which was compiled in her PhD dissertation for the Courtauld Institute of Art entitled, "A Critical Analysis of Artists' Handbooks, Manuals and Treatises on Oil Painting Published in Britain between 1800-1900: with a reference to selected eighteenth century sources", University of London, 1991), with the additional information from more recent investigations into the availability of specific resins during that period.
Anna Southall of the Tate Gallery delivered a presentation, "Turner's Contemporaries: Their Material, Practices and Opinion", which continues to present the context of the period. This presentation has been drawn from information in artists' notebooks and from Leslie Carlyle's doctoral thesis mentioned above. Additional information was gleaned during the preparation of 75 works for the exhibition, "Robert Vernon's Gift - British Art for the Nation, 1847", from both the conservation treatment and related investigation of varnishes, binders, and vehicles. The exhibition catalogue includes a technical essay with this information written by both Leslie Carlyle and Anna Southall.
Afternoon talks included a diversity of speakers from both the art historical and scientific specialties. Marianne Odlyha (Birkbeck College) presented "Thermal Characterization of Paint Samples from Turner's Opening of the Valhalla". Jaap Boon (FOM Institute for Atomic and Molecular Physics, the Netherlands) presented "On the Molecular Signature of Paint Samples from Turner's Opening of the Valhalla using Temperature Resolved PY-MS". "Natural Dyes and Pigments in the Earlier Nineteenth Century" was presented by Nicholas Eastaugh. Stephen Hackney (Tate Gallery) presented "The Condition of Turner's Oil Paintings". He spoke from experiences drawn from his past treatments of Turner's paintings in the collection of the Tate Gallery. Cecilia Powell presented the last talk of the day, "Turner's Sketches: Purpose and Practice".
The careful research done by these varied experts has yielded a valuable body of information for the conservation field. Both the PhD dissertations and the exhibition publications mentioned in this review are generous contributions to practicing conservators.Reviewer: