The Restoration of Paintings 3895089222, 9783895089220

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CELLULOSE GLUES mostly transparent yellow. Cellulose nitrate can be dissolved in most organic solvents. Rathgen used Zapon lacquer or dope (see below) to consolidate infested woods.26 Poppy-seed oil was used as a plasticizer. Camphor, castor oil and linseed oil were also used as plasticizers, but they had a tendency to produce undesirable signs of aging, such as "sweating" or embrittlement. Acetylcellulose is more durable and more stable than cellulose nitrate, and, by contrast with the latter, is not combustible. It is only soluble in acetone or acetone-alcohol mixtures and replaced cellulose nitrate as a consolidant. In the 1950s and 1960s cellulose acetate (dope) was frequently used as a preservative. Apart from resins dissolved in ethanol (like shellac), acetylcellulose was the first consolidant in the history of conservation to be dissolved in a highly volatile solvent (acetone). Highly volatile solvents can make wood swell so much that cracks appear. Furthermore, as the consolidant solution dries a hard layer forms in areas close to the surface and becomes increasingly thick, preventing the solvent from evaporating within the wood for a long time and giving rise to stresses in the support. The "fluid nylon" that was still used in the 1970s, calaton (Zellodyl), sometimes caused similar damage. According to Schiessl, water-glass, a soluble mass of potassium silicate (potash glass) or sodium silicate (sodium water-glass) was also used for the consolidation of sculptures, a completely unsuitable treatment.27 Aqueous cellulose glues, such as methylcellulose _r carboxymethylcellulose, came onto the market in 1931. These were colorless cellulose ethers that expanded strongly in water, but were not suitable for wood consolidation on account of their expansivity. From about 1950 artificial resin glues replaced the glutoline and casein glues that had been standard until then. Polyvinyl alcohols, polyvinyl acetates, polyvinyl methyl ethers, polyacrylic acids and phenolic resins, polyvinyl chloride, polyvinyl acetate, and polyacrylic esters, all dissolved in dispersions or emulsions, came onto the market as adhesives, binding agents, and consolidants. These products were used for wood consolidation even though their properties, their purity, their byproducts, what other components were polymerized with them, and what plasticizers, stabilizers, solvents, etc. they contained were unknown. These products were used for wood consolidation. The problems that can arise due to the use of these agents were often overlooked or disregarded. The basic problem is the water that is added to these artificial resins as a dispergent. Further difficulties are caused by the fact ARTIFICIAL RESIN 44

GLUES

WOODEN SUPPORTS that some plasticizers and their derivatives are capable of migrating into the original substance, as well as the way that the binding agents age, a process about which there is insufficient information. During consolidation with an aqueous binding agent its water content causes expansion inside the support. Cellulose ester consolidants begin to dry on the outside, forming a layer that is impermeable to water vapor. As a result, a large proportion of the moisture present is trapped in the wood for a long time. It is generally accepted that, when dispersion polymers are used as consolidants, the size of the particles often prevents the consolidation of deeper layers, the wood often expands on account of their water content, and cracks can appear in the wood during drying. In addition to polymer wood consolidation, early on there was work on the possibility of consolidating wood using monomers, with polymerization taking place inside the wood. As monomers need no solvents, they have the advantage that the consolidant loses none of its volume. Heat, a catalytic adjuvant, or a particular type of radiation are required if monomers are to polymerize. In the 1940s consideration was given to the consolidation of unstable wood by this method. When it was first discussed a temperature of 212°F (100°C) was needed for setting, which meant that monomers were not suitable for the restoration and conservation of artworks and cultural treasures. In the 1960s there were attempts to consolidate wood with radiation-polymerized plastic monomers. Other monomers are what are known as cold-setting reaction resins, which are hardened by a catalytic adjuvant. Thelepoxy resins are among the members of this group used in restoration work. Since the early 1960s types of epoxy resin have been used in the most varied areas of conservation. Their greatest advantage is their slight change of volume after polymerization. The problems caused by these materials are related to their sometimes very high reaction temperatures (up to 230°F (11 O°C). At these temperatures the wood that has not been penetrated by the consolidant begins to dry out where it borders on damaged areas. Another early problem was their high viscosity, which meant that the resin flowed too slowly to penetrate deep into the wood. Formulations for thinning epoxy resins have been available since 1967. However, thinning has the disadvantage that it can make setting even slower. MONOMERS EPOXY RESIN! Wood consolidation today ON RESINS

Despite intensive tesearch into methods for the consolidation of biologically damaged wood, there are still no procedures for treating bored wooden supports that can be recommended unreservedly. The difficulties raised by all wood consolidation techniques are still connected with: . consolidant penetration . wood discoloration . wood expansion . reaction temperatures . their effects on the picture layer. One, if not several, of these problems usually arises when supports are consolidated. Hitherto, restoration and conservation work involving wood consolidation as described above has been based on the introduction of consolidants into damaged areas and cell cavities. Today it is most common to use artificial resins dissolved in organic solvents and monomers like the epoxy resins, which are polymerized by chemical catalysts. Wood consolidants dissolved in organic solvents include acrylic resin solutions such as Basileum LX Hardening, which uses the solvent tetrachloroethene (perchloroethylene). Some other common solvents are toluene, xylene, and high boiling white spirit. They are particularly associated with two of the problems discussed above: . the solute polymers dry physically, which means that there is a reduction of volume during consolidation, sometimes \ causing stresses and cracks in the artwork; . the solvent may affect certain substances in the artwork, such as the color layers. The problems of the past with regard to epoxy resins have been overcome. There are now cold-setting, thin epoxy resin products that are well suited to the consolidation of worm-infested wood. The procedure by which the two components are introduced into the wood together requires exact planning and execution in order to achieve optimal setting and penetration depth. When using reaction resins, it should be noted that polar solvents such as methanol can sometimes set off an uncontrollable acceleration in the consolidation process. Nonpolar solvents such as xylene or toluene do not cause reactions of this kind. The consolidants in current use are mostly biocidefree solutions of a setting substance in an organic solvent. Some of the solvents used themselves possess a certain insecticide effect, but this is hardly sufficient for conclusive eradication. The use of a combination of wood preservatives and consolidants is currently rejected by restorers. It is thought impossible to combine the active agents in such a way that they do not retard each other's action. Restorers still adhere to the principle of fighting the pest first, then consolidating the wood. The consolidation of wood damaged by fungi

The consolidation of wood damaged by fungi is usually undertaken with artificial resins. These viscous solutions penetrate very effectively, thanks to the porosity of wood that has been infested with fungi. If a slow-evaporating solvent is used, distribution is good in damaged wood. Insufficiently concentrated solutions reduce wood strength. Due to the great increase in the weight of the wood during consolidation, wood fibers that hang together loosely are pushed apart. A small amount of resin may not compensate for this loss of stability. Encouraging results have been achieved in tests with medium- to high-concentration artificial resin solutions in high boiling benzenes (Plexigum P28, 30-40% dissolved in high boiling white spirit [2843_2°F, 140-200°C]; Mowilith 30, 20% dissolved in toluene). Very good consolidation was achieved with the ready-prepared product Lignol AS/AW-K,28 SOLUTE ARTIFICIAL RESINS The consolidation of wood infested by larvae Wood that has been infested with insect larvae is weakened by frass galleries, but not chemically altered like wood attacked by fungi. In experiments carried out by Cuany et al. the best results were achieved with low-viscosity epoxy resins (such as Araldite BY158/Hardener HY22996). They remain fluid for a long time, distribute well, and consolidate the bore dust present in the frass galleries. Good consolidation is also obtained with thin artificial resins of medium (20-30%) concentration (Plexigum P28, 30% in high boiling white spirits; Paraloid Bn, 20 % in toluene3O). High-viscosity artificial resin solutions do not attain sufficient penetration and only bond the frass close to the surface. Weak artificial resin solutions transport too little consolidant into the damaged wood. It is possible to pretreat damaged wood with a weak, highly penetrative solution and then undertake the consolidation with a concentrated solution. Restorers are sometimes faced with wooden panels that have been consolidated in the past but are failing again. Before repair, checks should always be carried out to discover whether the consolidant intended for use will be compatible with the consolidant already in the wood. WOOD CONSOLIDATION 45

EVALUATION painting transferred to a new support made of textile, wood, or artificial composite boarding (fiberboard, blockboard). The reasons for this 'intervention are extensive damage to the original support by insects and/or chronic paint layer cleavage. It is not known when partial transfers were carried out for the first time. Total transfer is an invention of the 18th century. For a long time Robert Picault was regarded as its inventor. He transferred a Madonna by Raphael, which is now in the possession of the National Gallery in London, from wood to canvas in 1751 (see illustration on page 69), as well as many other important paintings. Research by Schaible has now proved that Italian painters and restorers were transferring paintings long before Picault.38 Every form of transfer is a last resort and should only be used if the painting cannot be preserved by any other means. The choice between partial and total transfer has always been a point of dispute among restorers. The apparently less hazardous method of partial transfer has often been chosen but, in my opinion, many restorers have overlooked the fact that it does not eliminate the original reasons for the transfer (see above) because a thin layer of the original panel is left in place. In total transfer the factor that is causing the problems, the wood, is eliminated and the picture layer fixed onto a new support. When unqualified total transfers are carried out the panel painting loses its characteristic features and structures and takes on those of the new support (see illustration on page 68). Partial transfer PROCEDURE Partial transfer is a procedure in which a wooden support is reduced until it is only 0.5-1 mm thick and the thin "support sheet" thus created transferred onto a secondary support. The reasons for partially transferring paintings are the same as those for mounting on secondary supports (see pages 56f.). Partial transfers are mentioned in the literature on restoration and there are paintings in collections that have been partially transferred, but it is a historical technique and other methods should be used today. Partial transfer involved three main procedures: . reinforcing the picture layer by sticking a covering onto it (facing) . reducing the original support to the desired thickness . gluing the reduced support onto a secondary support.

As restorers have to deal professionally with paintings that have been partially transferred, we will quote a (shortened) report of a partial transfer by one of several possible techniques that was carried out in 1952 at the renowned Courtaulds Institute in London. This example will demonstrate what panel paintings are expected to undergo during partial transfer. The picture side was protected with two layers of a strong silk paper, which was smoothed with a heating tool and a mixture of unbleached beeswax and colophonium. A wick, band of silk paper was allowed to protrude all round the panel. The faced painting was laid face down on a high-density board and the protruding strips of silk paper were fastened onto the rear side of the high-density board with adhesive tape. (This was to stop particles of wood finding their way between the picture layer and the paper.) The whole thing was laid front side down on a table and fastened with a cushioned board and screw cramps. A gouge was used to pare the support both with and across the grain until only half a millimeter was left, which was smoothed with sandpaper. The ground, the paint layer, and parts of the support were impregnated as much as possible with a mixture of unbleached beeswax and dried chalk using the warmed heating tool. The frass galleries and other irregularities in the wood cut open during the planing of the panel were filled in the same way. The secondary support chosen was a 0.5 in (12 mm) thick fiberboard somewhat larger than the painting. This board was impregnated with unbleached beeswax in a bath on the heating table. Then the warm secondary support was coated with a mixture of unbleached beeswax and chalk. The secondary support was allowed to cool off slowly to the point at which the wax/chalk coating was just sticky enough to ensure good adhesion to the reduced support which _as laid on it. The whole thing was then ironed together through a layer of parchment with a sheet of felt over it, working out from the center with a cold iron. The partially transferred painting was weighted down overnight with a board and weights,39

Total transfer There are two methods of total transfer. The first is the very risky one used by Picault and cited above, in which the picture layer is softened and then pulled away from the support like a stamp, although the descriptions that have been passed down of Picault's technique do not go_into great detail. The second method is the procedure that is still used occasionally today, in which the support is pared down by shaving to the ground or the paint layer (see illustration on page 68). Transfer should only be undertaken: C' TRANSFER 67

PASTE give exact proportions because they depend on the precise ingredients used. The lukewarm ground mixture is then applied with a brush to a thickness of about 1 mm. After it has dried a fine napless gauze is laid on top and bedded down with a layer of the ground mixture. This then has to dry. Next the painting is lined with a coarse canvas. The following paste is recommended: 1 part linseed flour mixed in 24 pans water, add 2 parts joiner's glue and boil for 30 minutes in a water bath; mix together 3 parts wheat flour and 3 parts rye 'flour and add to the paste. The whole mixture is sieved and boiled for some minutes in a water bath. Before it goes cold 1 part molasses can be added to make the paste more elastic. The "sandwich" is turned over and the plaster bed is removed. The plaster holding the protective layers in place is softened with water and a bristle brush, and the plaster mixture rubbed off down to the canvas. The canvas weave can then be rolled off. The waxresin mixture is softened with white spirit and removed with cotton wool. Lastly, the handkerchief linen is carefully rolled away from the paint layer. The transferred painting is then nailed onto a blockboard or chipboard sheet in the same way as a canvas painting.4O RENEWING DAMAGED SUPPORTS PUTTIES Only a few panel paintings in German collections have been so badly damaged by fungi or insects that their wood has had to be renewed. It is no longer possible to ascertain when and where panels were first renewed. Presumably, damaged wood has always been removed and replaced with new material, or putties used to renew damaged parts. Wooden supports damaged by the larvae of insects react sensitively to impacts or pressure. Not only the corners are at risk but, depending on the extent of the damage, the whole picture layer (see illustrations on facing page). According to the type and extent of the damage and the attitude and training of the restorer involved, supports are transferred (see pages 65ff.), consolidated (see pages 40ff.), and/or renewed. As in the past, this is done with wood or putty. Putties are made up of filler(s) and binding agent(s). They are applied to defects with a

spatula. The fillers 70 WOODEN SUPPORTS that have been used include: sawdust, chalk, and, today, club moss spores and micro balloons; the binding agents used include wax, glutoline glues, PVAC dispersions, Paraloid Bn, and epoxy resins (such as Araldite 2020). Depending on the binding agent, putties contract more or less strongly (the exceptions being wax and the epoxy resins) and have to be applied in layers (if the defect is deep) to prevent them tearing as they dry. Damaged areas on the back of a support, and eroded edges and corners are filled with putty. Wooden dowels and metal nails are used to stabilize the putty at the edges and are driven into the original wood. The putty is applied around the pins and smoothed to match the support. Putties do not react to changes in relative humidity in the same way as panels. Puttied areas in a panel can act like inelastic plugs, rise up, or even come loose where they meet the wood of the support. The edges and/or corners of a few panel paintings have been mended with slats or buttons. For this purpose the original substance is removed from the damaged areas, creating a surface onto which the replacement parts can be glued. Renewing supports with wood is a historical technique. Compared to puttying, it has the advantage that a material is used that looks and generally behaves like the damaged support, provided the correct wood is selected. In 1977-78 Bachmann renewed some of the wood on a panel from the Lindenhardt Altarpiece without straightening the original.41 Muller and Heiduk Vrana have subsequently refined this method.42 Using prefabricated strips of balsawood that always give a cross-section of 5 mm when glued together (for example, 2 x 2, 2 x 3, 2 x 5, 3 x 5, 3 x 3, 5 x 5), they are able to assemble a lining that fits well and reduce the amount of work required. The binding agent used is a dispersion glue. The new inserts can usually be fitted so precisely that they do not have to be glued to the original and can be removed at any time (see illustration on page 71). PROTECTIVE BACKINGS Protective backings are intended to protect a painting against mechanical and environmental influences. They are applied directly onto the support or fitted behind it (see illustrations on the left, on facing page and on page 74). We distinguish between direct and indirect protective backings. Direct protective backings consist of a protective layer attached firmly to the support.

Indirect WOOD BALSA WOOD STRIPS On facing page: This panel (1) has been badly damaged by insects, as is shown clearly by the computer tomography scans (2, 3). During restoration the damaged area was opened (4, 5), lined on both sides with short strips of wood (6, 7) and sealed up again (8). A computer tomography scan made after the work was completed shows defective areas filled with wooden strips (9). (Icon, private collection)

OW PROTECTIVE ACKINGS WORK is suitable for this purpose needs to be decided in each individual case. The same is true of Styropor on account of its lack of stability. 67 An indirect protective backing delays a panel's reactions to alterations in relative air humidity by forming a climatic pocket between the reverse of the painting and the backing board. This protects the support against short-term variations in temperature and/or humidity. The duration of the protection is dependent on the type of board, in particular on its expert mounting on the back of the painting, its vapor resistance coefficient (m), its thermal conductivity, and sometimes its hygroscopicity. If paintings have been in an unfavorable climate for some time (too dry or too humid), protective backings influence their adjustment negatively. A certain period of time goes by before the lower or higher humidity in the climatic pocket has equalized with the more favorable climate. In other words, protective backings delay the reaction of wooden supports to climatic changes of all kinds. To a certain extent, a good protective backing can protect a wooden support from "rhythmic," short-term climatic variations, but it offers no protection against climatic variations that take place over longer periods of time. By contrast with works on textile supports, mechanical protection plays only a secondary role for panel paintings. The protective backing on a textile support is supposed to protect it from vibrations and knocks; on wooden supports it serves mainly to balance the pressure exerted when the picture is framed, with spring clips, for example. The local compressive forces of the spring clips are absorbed and distributed over a wider area. MECHANICAL PROTECTION HANGING, EXHIBITION Panel paintings are hung, stored, or exhibited in various ways, depending on their significance, size, sensitivity to climatic conditions, and similar factors (see illustration on page 76). Hanging is the term used specifically when paintings are fastened to a wall with nails, wires, or comparable materials. Depending on their location and/or construction, walls may be drier or moister and/or cooler or warmer than the ambient air in the gallery. These properties are sometimes transmitted to the whole artwork and may cause serious damage if it is hung incorrectly. This fact was well known to artists and restorers from as early as the 17th century, as can be readily seen from surviving documents, written sources, and labels on protective backings on paintings. In 1834 Welsch advised that small pieces of cork should be glued onto the back of the decorative frame of a painting to hold it away from the wall and protect the artWork

against temperature variations and wall moisture.68 Lucanus (1832)69 and Voss (1899)70 also wrote extensively on this topic. This is a clear indication that the problems associated with the moisture and low temperatures of walls were generally familiar by the 19th century. In the 20th century this topic has been dealt with by Wolters (1955 and 1960),71 Nicolaus (1979 and 1986),72 and Schaible (1987),73 Schaible suggested that, if walls are in a particularly poor state, the wall itself can be insulated behind the panel with additional cork or foam sheeting. It is usually enough to hang the picture at a certain distance from the wall to protect it from the influences of a cold and/or damp wall. This is done by attaching buttons or corks to the back of the decorative frame. A gap of 0.2-1.5 in (0.5-4 cm) is suggested in the literature,74 What is crucial is that the gap between the wall and the painting is large enough for the air to circulate behind the painting. Correct hanging can make a decisive contribution to ,the preservation of a painting. Highly climatically sensitive panel paintings, such as Titian's Christ and the Tribute Money in Dresden, are exhibited in what are known as climatized exhibition cases, in which the climate necessary for the preservation of the painting is created with special salt solutions or silica gel. PROTECTIVE BACKINGS CORK CUSHIONS CLiMATIZED EXHIBITION CASES Overleaf: The altarpieces in the Wallraf-RichartzMuseum in Cologne are placed at a considerable distance from the wall. This ha: the advantages that the wooden panels an not influenced climatically by the wal and, in addition, visitors can see the painted backs of the altar wings. 75

Notes C. Wolters, The care of wood panels, in: Museum, 8, 3 (1955), pp. 139-164 U. Lohmann, Holzhandbuch. Rosenheim 1986, p. 13 D. Grosser, Pflanzliche und tierische Bau- und Werkholzschadlinge. LeinfeldenEchterdingen 1985, p. 18 The Swedish engineer Johann August Brinell (18491925) developed what is known as the impression test, in which a ball is pressed into a material in order to determine its hardness. F. Kollmann, Technologie des Holzes und der Holzwerkstoffe. Vol. 1, Berlin 1951, p. 392 D. Grosser, see note 3, pp. 28ff. Anon., Holzwurmsuchgerat "Detektiv, " ein neues Hilfsmittel der Holzindustrie, in: Umschau in Wissenschaft und Technik, 7 (1951), p. 219 In this book I follow the excellent survey of the applications of biocides given by U. Schiessl in his study: Historischer Oberblick Ober die Werkstoffe der schadlingsbekampfenden und festigkeitserhohenden Holzkonservierung, in: MaltechnikiRestauro, Vol. 90 I (1984), pp. 9-40. I Vitruvius, De architectura. Vitruvius, a Roman architect and engineer, composed this work, which consists of ten books, and is based on Greek writings, in about 25 Be. It discusses architecture, clockmaking and mechanics, and is the only theoretical architectural handbook to have survived from antiquity. Leonardo da Vinci, Das Buch von der Malerei (1492). Deutsche Ausgabe nach dem Codex Vatican us 1270, Obersetzt und Obersichtlicher geordnet von H. Ludwig (reprint of 1882 edition). Osnabruck 1970, quoted in: A. Eibner, Entwicklung und Werkstoffe der Tafelmalerei. Munich 1928, p. 97 G. G. Zinke, Kunst allerhand natOrliche Korper zu sammeln, auf eine leichte Art fOr das Kabinett aufzuarbeiten und vor der Zerstorung feindlicher Insekten zu sichern. Jena 1802 Carbolineum: the term was formed by the combination of the words "carbo" (coal) and "oleum" (oil). It is a mixture of the petroleum products phenol and cresol. Instructions for Xylamon Holzwurm- Tod manufactured by Desowag To "restore" the blackened parts they were wrapped in cloths soaked in hydrogen peroxide. This converted black lead sulfide into white lead sulfate. H.-P. Sutter, Holzschadlinge an KulturgOtern erkennen und bekampfen. Berne 1986, p. 111 L. A. Zycherman/J. R. Schrock (eds), A Guide to Museum Pest Control. Foundation of the American Institute for Conservation and Association for Systematic Collections, Washington DC, 1988 Ageless Oxygen Scavenger is available from Conservation Materials Ltd., P. O. Box

2884, Sparks, Nevada 89432 F. Rathgen, Die Konservierung von Altertumsfunden. Parts II and III. Berlin 1924, pp. 140ff. The Keylwerth Diagram was originally developed by W. K. Loughborough and converted into German measures by R. Keylwerth. It sets out the correlations between vapor pressure and relative air humidity as well as between relative humidity and wood moisture. The graph on page 20 shows a simplified form of the diagram. F. MOlier-Skjold, Zur Frage der Schadigung von Gemalden durch Rontgenstrahlen, in: Angewandte Chemie, 49 (1936), pp. 161-162; 50 (1937), pp. 321ff. 21 V. CuanyN. Schaible/U. Schiessl, Studien zur Festigung biologisch geschwachten Nadelholzes: Eindringvermogen, Stabilitatserhohung, feuchtephysikalisches Verhalten, in: Zeitschrift fOr Kunsttechnologie und Konservierung, 3, 2 (1989), pp. 249-292 22 Ibid., p. 277 23 F. Rathgen, see note 18, p. 148 24 D. Rosen, The preservation of wood sculpture: the wax immersion method, in: Journal of the Walters Art Gallery, 13/14 (1950/51), pp. 45-71 25 F. Rathgen, quoted in U. Schiessl, see note 8, p. 27 26 F. Rathgen, see note 18, p. 148 27 U. Schiessl, see note 8, p. 22 28 KD-Chemicals, Laupen, Switzerland 29 200 9 of Araldite is added to 256 9 of a solvent mixture made up of 75% xylene, 15% isopropanol and 10% ethyl acetate, then 56 9 of the setting agent Araldite HY 2996 is added. 30 Paraloid B72 is a polymethyl methacrylate (PMMA) dissolved in toluene for wood consolidation. 31 R. E. Straub, A modified apparatus for fe-joining heavy panels, in: Studies in Conservation, 2 (1955/56), pp. 192ff. 32 U. Niedermann, Einfaches Hilfsgerat zur Verleimung von Fugen und Rissen, in: MaltechnikiRestauro, 1 (1979), pp. 51-54 33 Willard Developments Ltd., Chichester, England 34 L. Hacquin, quoted in: V. Schaible, GemaldeObertragung, in: MaltechnikiRestauro, 2 (1983), pp. 96-129 35 R. Carita, Patricia della parchettatura, in: Bolletino dell' Instituto Centrale del Restauro, Vol. 27/28 (1956), pp. 103-131 . 36 R. D. Buck, Some applications of mechanics to the treatment of panel paintings, in: G. Thomson (ed.), Recent advances in conservation. London 1963, pp. 156-162 37 e. Wolters, see note 1

38 V. Schaible, see note 34 39 Cf. P. J. F. M. Hermesdorf, Ein neues Verfahren zur Obertragung von Tafelmalereien bei teilweiser Beibehaltung des Bildtragers: in R. E. Straub (ed.), Ober die Erhaltung von Gemalden und Skulpturen. Stuttgart, Zurich 1963, pp. 87-98 40 Cf. K. E. Denninger, Ein Verfahren zur Obertragung _italienischer Tafelbilder des 13.-15. Jahrhunderts, in: R. E Straub (ed.), see note 39, pp. 99-106 41 H.-w. Bachmann, quoted in: N. Erhardt, Moglichkeiten der Erganzung groBer Fehlstellen an frassgeschadigtem Holz. Degree dissertation. Cologne Fachhochschule, 1995, p. 13 42 MOiler and Heiduk Vrana, quoted in: N. Erhardt, see note 41, p. 16 43 R. D. Buck, The use of moisture barriers on panel paintings, in: Studies in Conservation, 6 (1961), pp. 9-19 44 P. Achternkamp, Der ROckseitenschutz von Gemalden: Historische und zeitgenossische Praxis, in: Zeitschrift fOr Kunsttechnologie und Konservierung, 5 (1991). p. 18 (see reference in note 55) 45 e. Koster, Ober die Restauration alter Olgemalde. Heidelberg 1827, p. 14 46 F. Bentz, Ratschlage zur Konservierung von Gemalden und Zeichnungen, in: Jahrbuch fOr Kunst und Kunstpflege, 1915-21, p. 335 47 J. Basch-Bordone, Handbuch der Konservierung und Restaurierung alter Gemalde. Munich 1921, p. 12 48 K. Wehlte, ROckseitenschutz fOr Gemalde, in: Die Kunstkammer, 5 (1935/36), p. 21 49 R. D. Buck, see note 43 50 e. Wolters, Treatment of warped wood panels by plastic deformation; moisture barriers; elastic supports, in: G. Thomson (ed.), see note 36, pp. 163-164 51 R. H. Marijnissen, Degradation, conservation et restauration de I'oeuvre d'art. Brussels 1967, p. 334 52 M. S. Brommelle/A. E. Werner, Problems of conservation in museums, in: ICOM, London 1969 53 M. Koller, Barocke Altarbilder in Mitteleuropa: Technik, Schaden, Konservierung, in: Der Altar des 18. Jahrhunderts. Das Kunstwerk in seiner Bedeutung und als denkmalpflegerische Aufgabe. Forschungen und Berichte der Bau- und Denkmalpflege in BadenWOrttemberg, Vol. 5, Munich. Berlin 1976, p. 210 54 J. A. Brewer, Effect of selected coatings on moisture sorption of selected wood test panels with regard to common panel painting supports, in: Studies in Conservation, 36 (1991), pp. 9-23 55 P. Brunner, ROckseitenschutz von Gemalden. Degree dissertation. Staatliche Akademie der Bildenden KOnste, Institut fOr Technologie der Malerei, Stuttgart,

1988 (Achternkamp is Brunner's married name, see note 44) 56 H. Mogford, Hand-book for the preservation of pictures. London 1845, p. 28 57 A. H. Church/H. W. Ostwald, Farben und Malerei. Munich 1908, p. 324 58 e. Wolters, see note 50 59 J. A. Brewer, see note 54 60 F. Bentz, see note 46, p. 338 61 R. E. Straub, Das Problem des verwolbten Holztafelbildes, in: Nachrichtenblatt der Denkmalpflege in Baden-WOrttemberg, 11 (1968), p. 74 62 W. Brandt, Lokaler Klimaschutz im Tafelbild, in: Nachrichtenblatt der Denkmalpflege in Baden WOrttemberg, 11 (1968), p. 78 63 P. Achternkamp, see note 44, p. 40 64 Tycore, marketed by Anton Glaser, Stuttgart 65 Deko-Leichtplatte, marketed by Karthauser-Breuer GmbH, Cologne 66 e. Schulze-Senger/H. W. Schwarz, Zur Stabilisierung begradigter einseitig bemalter Eichenholztafeln, in Mitteilungen des Deutschen Restauratorenverbandes (DRV), 7 (1985/86), pp. 98-102 67 Styropor is a proprietary brand of polystyrene rigid foam. 68 F. Welsch, Vollstandige Anweisung zur Restauration der Gemalde in 01-, Wachs-, Tempera-, Wasser-, Miniaturund Pastillenfarben. Quedlinburg, Leipzig 1834, p. 85 69 F. G. H. Lucanus, GrOndliche und vollstandige Anleitung zur Erhaltung, Reinigung und Wiederherstellung der Gemalde. Halberstadt 1832, p. 20 70 E. Voss, Bilderpflege. Leipzig 1899, p. 14 71 C. Wolters, see note 1; C. Wolters, The care of paintings: fabric paint support, in: Museum, 13,3 (1960), p. 142 72 K. Nicolaus, DuMont's Handbuch der Gemaldekunde. Cologne 1979, revised edition 1986, p. 28 73 V. Schaible, Neue Oberlegungen zur Feuchtigkeit am Leinwandbild, in: Zeitschrift fOr Kunsttechnologie und Konservierung, 1, 1 (1987), p. 93 74 P. Achternkamp, see note 44, p. 28 NOTES 77

MATERIALS FOR SUBSTRUCTURE TREATING IRREGULARITIES TREATING SEAMS REMOVING EDGES

OF FABRIC Knots, thickenings in

the thread, and (as here) a seam will very often manifest themselves on the front of a painting. Fabric knots and seams Textile supports and lining fabrics may - depending on the quality, age, and size of the fabric - have knots, thickened threads, and/or seams (illustration facing page and right). Knots, thickened threads, and seams form irregularities on the verso of a painting that, when the painting is lined, would push through and become visible on the front. The result would be perceptible "knots" in the picture layer and/or bulges along the seam (illustration page 92). To prevent such irregularities from pushing through, textile supports need to be prepared for lining, usually with what is called a "substructure." Substructures are made of thick, soft materials in which knots and bulges are able to embed themselves. If they are still not absorbed, even by an appropriate substructure, they are removed with a scalpel and/or sandpaper. This of course weakens the stability of the thread and hence the stability of the textile support. To reduce irregularities, the verso of the painting or lining fabric is coated with primer or a mixture of Beva 371 and chalk. This will fill in the interstices of the fabric, leaving irregularities visible as projections; these are then smoothed off Another way of' embedding irregularities is by using thicker lining material or interposing a layer of soft fleece (the "sandwich" method). The textile supports of large paintings often consist of two or more strips of material sewn together, with the seam forming a bulge on the verso of the painting. Unless suitable preparations are made prior to lining, or appropriate lining techniques are employed, the seam will press through and become apparent on the front of the painting. Picture restorers have a number of ways of lining paintings with seams in the support: . The seam is secured on the front of the painting (facing), the projecting edges of the seam on the verso (illustration facing page) are removed with a scalpel, and any minor irregularities are rubbed off with sandpaper.

. The painting is lined on a low-pressure or vacuum hot table with the picture layer downward. The lining canvas "hugs" the seam. This deforms the verso of the painting, but leaves the front smooth. . Lining is done in a vacuum envelope. Again, the lining fabric hugs the seam. Deformation occurs on the verso of the painting, but usually there will also be some slight deformation on the front. Removing the projecting edges of fabric from a seam is a major operation. Often the sewing thread also gets damaged in the process, destroying the join between the two strips of canvas. If this is not spotted in time, when the lining fabric is later removed and if

GENERAL RESTORATION OPTIONS 91

WOOD PANELS PASTEBOARD BLOCKBOARD FIBERBOARD CHIPBOARD ALUMINUM

SHEETING

NOOD PANEL EFFECT IMPRESSION INTO THE PICTURE LAYER 1955 Straub described as marouflage a procedure in which the thin wooden support of a mummy picture from the Ancient Egyptian site of El Faiyum was bonded on to a sheet of five-ply plywoodJ8 De Wild described the marouflage technique in 1964 and by doing so will presumably have encouraged others to copy itJ9 Just one year later, in 1965, Straub was warning against marouflage.80 Until the beginning of the 20th century, wood panels, pasteboards, and metal sheets were the only materials available for use as auxiliary supports for marouflage. The beginning of the 20th century brought new, artiucially manufactured sheeting materials, such as plywood, blockboard, chipboard, high-density fiberboard, and aluminum sheeting. The classic auxiliary supports for marouflage were wood panels. Depending on the size of the painting to be marouflaged, they were made up of one or more boards glued together. As a rule, glutoline glues were used for marouflage. In the 19th century pasteboards were used as auxiliary supports for canvas paintings. Plywood began to be produced on an industrial scale in Germany and used as a support for marouflage from about 1900 onward. Blockboard is made of rectangular-section wood batons pressed between several layers of veneer. It was used frequently for partial and total transfers of wooden panel paintings in the 20th century. It is also found occasionally as an auxiliary support used in marouflage. Fiberboards produced from wood shavings have been available since about 1914. They are classified as either low-density or high-density fiberboards. Highdensity fiberboards are used for marouflage. Chipboards were first described in 1943 and produced on an industrial scale from 1950 onward. They are used for the marouflage of large-format canvas paintings. In the 1960s aluminum sheeting also began to be used for auxiliary supports. Sheet aluminum81 or "aluminum honeycomb supports"82

were employed in marouflage. Every time marouflage is carried out, the characteristics of the support, what is known as the "wood-panel effect," are loSt.83 All paintings on wood, canvas, metal, or stone possess a quite specific structure which is dependent on the particular support used. A specialist can identify the support simply by looking at the surface of the painting (see illustrations above and on opposite page). When a painted fabric is transferred on to a rigid support some of its characteristic features are destroyed or influenced by the properties of the new support. Where marouflage has been carried out inexpertly, the picture layer is impressed into the interstices of 132 TEXTILE PICTURE SUPPORTS

the original fabric. As a result, the structure of the fabric can be seen in the picture layer and influences the surface structure of the painting. Damage of this kind is found not only on marouflaged paintings, but also when paintings have been lined in heat/vacuum tables, in which powerful forces are exerted on the surface of the painting. During marouflage the picture layer is particularly at danger because the painting is pressed onto its new, hard auxiliary support without any cushioning beneath it to reduce the forces which arise. If a painting displays pronounced impasto, the facing is not soft enough, and the adhesive is applied too thickly, what is known as "negative- effect damage" occurs. If the facing is inelastic, pressure is not NEGATIVE EFFECT DAMAGE

distributed evenly across the whole surface of the painting as the press is tightened, but only bears upon areas of impasto in the picture layer, which then sink into the adhesive layer. The adhesive under these areas of impasto is pressed away sideways and forms bulging pockets of adhesive which lift up the flatter areas of the picture

layer nearby. This "levels" the paint layer, which is causing the painting to lose its original surface structure. Negative-effect damage is not restricted to marouflage, but can occur whenever smooth supports are used in lining. Marouflaged paintings sometimes warp. They distort in this way if aqueous adhesives are used without the attachment of a protective interleaf to the reverse of the support. Above and on oppositEO-page: Paintings on textile supports (above) and wooden panels (opposite page) have their own cha racteristic structures which are destroyed by marouflage or transfer.

Nails and Staples 147 Notes 152 THE PAINT LAYER 154 Introduction 157 Changes caused by Painting Techniques 158 Wrinkling 158 Yellowing 158 Loss of opacity 162 Fading and browning 163 Buckling 164 Craquelure 165 Drying cracks 167 Aging cracks 174 Cracks in paintings on canvas 179. Cracks in wood panel paintings 183 Blanching 184 Artificial craquelure 185 Layer Separation, Binding Agent Failure 189 Wooden picture supports 189 Textile picture supports 194 Metal picture supports 199 Copper plares 199. Iron panels 200 Heat blisters 200 Damage caused by acids and stripping agents (through vandalism) 203 Damage by microorganisms 204 Reattaching and Securing Separated Layers 207 Wooden picture supports 212 Piercing merhod 214. Hinge method 216. Immersion method 216. Funnel method 217. Layer reattachment on badly damaged supports 217. Treatment of powdering or chalking color layers 217 Textile picture supports 221 Treatment of air pockets 224 Metal supports 224 Copper plates 224. Iron panels 224 Treatment of paintings damaged by acid and paint stripper 225 Treating burn blisters 226

Combating microorganisms 227 Binding agents 229 Natural aqueous binding agents 229 . Forms of wax 230 . Oils, resin, balsam 230. Synthetic binding agents (Polyvinyl alcohols [PVAI) . Polyvinyl acetates (PVAC) . Acrylic resim. Cellulose ethers. Calaton [nylon} . Beva 371) 231 Wetting agents 234 Filling 233 Preparation of the defective area 235 Filling putty 235 Fillers with natural drying agents (Glue filler. Oil filler. Wax filler) 238 . Fillers with synthetic binding agents (Beva filler. Polyvinyl alcohol filler. Polyacrylic filler. Readymade filling putty) 241 Treating the surface 243 . Applying the filler 243 . Leveling-off 243 . Structuring 243 (Structuring with filling putty. Structuring on filling putty) 244. Coloring 251 . Isolation 253 Treating old fillings 253 Filling substances 253 Binding agents 254 Preservatives 256 Retouching 257 Retouching techniques 260 Construction of retouchings 262 Pigments (Opacity. White. Blue. Yellow. Red. Brown. Black) 263 . Binding agents 270. Retouching paints 272 Retouching with drying oils and resins 274 Retouching with oil paints 274. Retouching with resinous paints 276. Resin-oil paint retouching 276 Retouching with aqueous binding agents 277 Retouching with vegetable gums 277. Watercolor ret6uching 277. Gouache retouching 278 . Egg tempera retouching 278 Retouching using semisynthetic and synthetic binding agents 281 Cellulose ether retouching 281 . Acrylic resin retouching 281 . Polyvinyl acetate retouching 282. Polyvinyl alcohol retouching 283 . Polycyclohexanone (ketone) resin retouching. 283 Structures 283 Artificial aging 284 Surface luster 285 . Paintbrush 289 Methods of completion 289 Retouching "fragmented" paintings 290. Neutral retouching 290. Tratteggio (rigatino) 291 . Standard retouching 294 . Total retouching 294. Overpainting

295 . Reconstructing lost forms 295 Craquelure 299 Patina 299 Varnishes 300 Workplace 303 Notes 305 VARNISH 308 Introduction 310 Varnishes 313 --------Oil varnishes 313 Oleo resinous varnishes (oil lacquers Albumen or egg white varnishes 31 Resin varnishes 314 Soft resin or resin essence varnishes 315. 316 . Wax and wax-resin varnishes 317. varnishes 318 Varnish Application 321 Swabbing 321 Brush application 322 Spray application 322 The Varnish Layer 325 Yellowing 328 Bloom 330 Embrittlement 331 Craquelure 332 Crazing 332 Surface Dirt 335 Air pollution 335 Deposits and adhesion 336 Protecting the surface of the paintin Cleaning 339 Solvents 339 Hazards 344 Protective measures 347 Surface cleaning 351 Regeneration 353 Varnish removal 356 Removal of retouches and overpaint Removing varnish with organic solvents (5, . Solvent triangle. Reftrming method) 359 . with solvent gels 366. Removing varnish 366 . Solvent gels or solvent emulsions 3/ 367 . Removal using powder 368 . Cleani 368 . Microfriction 368 Notes 370 APPENDICES

Documentation 372 Glossary 384 Bibliography 392 Illustration acknowledgements _ INDEX 408