Inpainting: Compensation for Gilded Surfaces

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The information presented on the Paintings Conservation Wiki is the opinion of the contributors and does not imply endorsement or approval, or recommendation of any treatments, methods, or techniques described.Compiler: Catherine A. Metzger
=Methods of Loss Compensation for Gilded Surfaces=
==Introduction==
Gilded surfaces, in which a thin layer of gold is attached to a support, can become worn through cleaning, handling, or general age and therefore sometimes may need to be repaired. While it may seem an obvious choice simply to replace an area of gilded loss using the same method by which it was first applied, this is not always possible or necessary. Methods of compensation vary widely. These include regilding by traditional or nontraditional means; application of powdered gold; and non-gold techniques in which paint, sometimes composed of powdered metal, is used to imitate the gilded surface. To fully reintegrate an area of gilded loss, it is often necessary to distress or tone a newly gilded area as described below. It is important to apply any compensation on top of an isolating layer. Thornton suggests SoluvarⓇ or AcryloidⓇ B-72 for isolating water gilding, while only Soluvar ., with its less polar solubility, is appropriate for isolating oil gilding. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 218.
The information below summarizes the most commonly used techniques for gilded loss compensation, including those used by past restorers and present-day conservators.
==Gilding Compensation: Superficial vs. Larger Loss==
To determine the best method for gilding compensation, it is first necessary to assess the extent of the damage, which generally falls into one of two categories. Superficial compensation is adequate for an area that has been scratched or mildly abraded so that the gilded surface alone is disturbed. More complicated compensation may be required when the extent of the loss is such that both the gilding and underlying surface are damaged or when the damaged surface includes raised gilding or ornamentation, such as punchwork or sgraffito.
===Superficial Compensation===
====Non-Gold Techniques====
Many of the non-gold compensation techniques now in use were first employed by Italian restorers who followed the lead of the early 20th-century Italian art historian Cesare Brandi, an advocate of reintegration that did not seek to conceal the damage completely. Brandi described this approach as the “second principle” in his book on art restoration theory: “Restoration must aim to reestablish the potential unity of the work of art, as long as this is possible without producing an artistic or historical forgery…” Bonsanti, G. 2003. Theory, methodology, and practical applications: Painting conservation in Italy in the twentieth century. In Early Italian paintings: Approaches to conservation. Proceedings of a Symposium at the Yale University Art Gallery, April 2002, ed. P. Garland. New Haven and London: Yale University Press. Pp 86 Even earlier, this approach had been suggested by other Italian art historians, such as Giovan Battista Cavalcaselle who wrote in 1877, “Wherever the colors are missing just lay a neutral tone nearing the original colors, but keeping it somehow below the vivacity of local zones”. Bonsanti, G. 2003. Theory, methodology, and practical applications: Painting conservation in Italy in the twentieth century. In Early Italian paintings: Approaches to conservation. Proceedings of a Symposium at the Yale University Art Gallery, April 2002, ed. P. Garland. New Haven and London: Yale University Press. Pp 83. A benefit of this methodology is that the conservator does not interfere with the original balance of the painting as a work of art or an historic document.
However, among the disadvantages is that non-gold techniques can never recreate the reflective surface of the original, resulting instead in a matte surface.
:1. Areas of lost gilding may be inpainted in a flat monochromatic color with yellow ochre or another neutral tone. The goal is for the eye to pass more easily over the area of loss without disturbing the balance of the original painting. The level of gloss can be adjusted by applying a surface coating or by the choice of paint medium. For example, Liquitex Matte Medium can be mixed with ochre watercolor paint to compensate for matte areas of water gilding, whereas Liquitex Gloss Medium can be tinted reddish brown with watercolors to restore burnished areas of loss. Moyer, C. and G. Hanlon. 1996. Conservation of the Darnault mirror: An acrylic emulsion compensation system. Journal of the American Institute of Conservation, 35(3):185–96. Pp 186.
:2. A variety of Italian techniques discussed in greater detail elsewhere in the Inpainting volume also may be used for gilded loss, either using paint alone or by adding metal powder or mica pigment in a “shell gold” technique (see below) to better replicate the light refraction of the original surface. Ciatti, M. 2003. Approaches to retouching and restoration: Pictorial restoration in Italy. In Early Italian paintings: Approaches to conservation. Proceedings of a Symposium at the Yale University Art Gallery, April 2002, ed. P. Garland. New Haven and London: Yale University Press. Pp 198.
:3. Proprietary acrylic iridescent paints are best used in situations where the gilding is abraded rather than completely lost, since these paints are fairly translucent and generally have low hiding power. They are made by Golden, Liquitex, and Hyplar, among others. Powdered iridescent pigments also are made to mix with a conservator’s choice of binding medium, but Thornton feels that the commercially prepared paints are more convenient and work as well. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 226-7.
:4. Metal powders traditionally have been used, but they should be avoided, since they tarnish over time. However, the tarnish process can be slowed by coating the metal powder with varnish. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 226.
====Gold Powder Techniques====
:1. “Shell” or powder gold may be mixed with weak gum arabic, weak size, or egg white and inpainted in an area of gilded loss. This often is more successful in a loss that was originally oil rather than water gilded. Green, M. 1979. Conservation and restoration of gilded antiques. The Conservator, 3, 39–42. London: ULIC. Pp 39-42. To keep the resulting surface from becoming too glittery, the powder should be as finely ground as possible.
:2. For a similar effect, finely ground mica powder may be mixed with various media.It is also possible to apply the binder first to the area of loss and then stipple the powder into the binder with a stiff brush before the medium dries. Moyer, C. and G. Hanlon. 1996. Conservation of the Darnault mirror: An acrylic emulsion compensation system. Journal of the American Institute of Conservation, 35(3):185–96. Pp 189.
====Mordant Gilding====
Mordant gilding using either traditional or nontraditional materials is an excellent means of reintegrating loss in areas that were originally mordant gilded, since it can provide an appropriate level of sheen and covering power for the affected area. Its uses are not limited to replacing mordant gilt areas, but it is not the best choice for gilding where punchwork or incised lines are present, since the mordant would fill the tooled areas during application, preventing a crisp impression.
:1. Oil
:Cennino Cennini describes the preparation of linseed oil, the traditional oil used for gilding, in his book sections on oil painting and mordant gilding. Cennini, C. 1960. The craftsman’s handbook (Il libro dell’arte), transl. D. V. Thompson Jr. New York: Dover. (Reprint of 1933 edition.) Pp 58, 96–8. When oil is used as the mordant, the oil or oil-resin mixture should be painted with a small brush in the desired design area and allowed to partially dry to a flexible, tacky surface. If gold is laid onto the oil mordant too soon, it will wrinkle and deform. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 221.
:2. Wax
:When the gilding is lost, but the original bole is present, a technique using a wax mordant may be used to recreate an area of loss. The wax used may be in the form of a neutral colored commercially prepared shoe polish, which contains wax and rosin. It is thinly applied to the area of loss, allowed to dry, and then polished with a soft cloth. The mordant can be activated by the warmth and moisture of a breath, after which the gold leaf is immediately laid down and tamped with dry cotton. After a few minutes the gold will have set, and the surface may be polished with dry cotton, resulting in a lightly burnished appearance similar to that of burnished antique gold. Dwyer Modestini, D. 2003. Approaches to retouching and restoration: Imitative restoration. In Early Italian paintings: Approaches to conservation. Proceedings of a Symposium at the Yale University Art Gallery, April 2002, ed. P. Garland. New Haven and London: Yale University Press. Pp 222.
:3. AcryloidⓇ B-72
:Similar in application to the oil gilding, AcryloidⓇ B-72 may be brushed onto a surface to act as a mordant for gold leaf. The B-72 should be allowed to dry completely and harden. Hardening time depends on the solvents used. Volatile solvents such as acetone will result in a fast drying time, while a slower evaporating solvent has the benefit of allowing the mordant brushstrokes to even out. Once sufficiently dried, the film may be reactivated with a solvent, such as petroleum benzine (alone if the film retains some solvent) or a mixture of 3:1 petroleum benzine:ethanol. The leaf may be applied immediately and tamped with dry cotton. Thornton suggests that this method works best on flat or slightly curved surfaces, since the solvent-activated surface does not stay tacky for long. The surface may be burnished with an agate or polished with dry cotton wool to the desired finish. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 222.
:4. Acrylic emulsions
:Acrylic emulsions are “surfactant-stabilized suspensions of high-molecular weight acrylic resin beads in aqueous medium”. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 222. Among this group of stable acrylic media are Hyplar, Liquitex, and the Rhoplexes. These media may be tinted with dry pigments or applied in their clear form.
::i. Hyplar, Liquitex, and RhoplexⓇ B-60-A 
::A thick layer of either Hyplar or Liquitex medium or a thin layer of Rhoplex B-60-A may be applied to an area of loss with a brush, taking care to avoid air bubbles in the film. Rhoplex B-60-A dries quickly, so care should be taken to apply the film evenly. The layer should be left to dry completely, at which point the gilder may activate it by rewetting it with water or by breathing onto the surface to fog the film. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 224. Once the fog clears, gold leaf should be laid onto the surface and tamped with dry cotton wool. This surface then may be gently polished with dry cotton wool. These acrylic emulsions are best used as mordants on flat surfaces, large areas of relief, and highlights, since the medium does not maintain its tack for long, limiting the amount of working time. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 224.
::ii. RhoplexⓇ N-580 mixed with RhoplexⓇ B-60-A 
::Rhoplex N-580 mixed with Rhoplex B-60-A increases the working time, since the N-580 maintains a tacky surface forever. Thornton suggests mixing them in equal parts to increase the hardness of the N-580, resulting in a mordant with a tack similar to traditional oil gilding. He also advises that the addition of “less than 1% of a synthetic surfactant such as Aerosol OT will keep the Rhoplex from beading up on a shiny surface”. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 224. The extra working time gained allows this technique to be used in more intricate areas of design.
===Larger Loss Compensation===
====Gesso, Bole, and Gold====
The traditional choice for deep losses in gilded areas is to compensate by applying layers of gesso, bole, and gold as described by Cennini. Cennini, C. 1960. The craftsman’s handbook (Il libro dell’arte), transl. D. V. Thompson Jr. New York: Dover. (Reprint of 1933 edition.). Pp 70–74, 79–82. The gesso should be built up to just below level with the surrounding surface to leave room for the bole. The bole should be made of a clay that best matches the original bole in color, applied thinly to the gesso in a series of layers, and allowed to dry completely. In preparation for gilding, the bole should be wetted with water by brush to reactivate it. The gold leaf may be laid down, covering an area larger than the loss so that the edges may be feathered to better blend with the original. Green, M. 1979. Conservation and restoration of gilded antiques. The Conservator, 3, 39–42. London: ULIC. Pp 40. Gold manufactured today is beaten by machine, creating a much thinner layer than that made in the early Renaissance. Modern gold leaf is typically 1/25,000-inch thick, Green, M. 1979. Conservation and restoration of gilded antiques. The Conservator, 3, 39–42. London: ULIC. Pp 40. and it is often advisable either to apply a double layer of gilding or to ensure that the gold used is thicker, as is Manetti Deep Double. Leonard, M. 2003.Artist/conservator materials: The restoration of a Predella Panel by Luca di Tomme. In Early Italian paintings: Approaches to conservation. Proceedings of a Symposium at the Yale University Art Gallery, April 2002, ed. P. Garland, 225–232. New Haven and London: Yale University Press. Pp 225–232. With this method of gilding, it is possible to recreate the punchwork or incisions in the area of loss, with the proper tools. Unfortunately, if the loss is too shallow, the fill may be brittle and a crisp punch may not be possible. Fly, L. E. and J. Klaar. 2004. Loss compensation for gilded surfaces using wax-resin fills. Postprints from the ANAGPIC Student Conference, Ottawa, Canada, April 2003. Kingston, Ontario: Queens University. Pp 6. Conversely, if the gesso fill is too deep, a crack pattern different than that of the original surface may occur in the fill area on drying.
====Polyvinyl Alcohol====
In Thornton’s chapter in Gilded Wood: Conservation and History, he mentions a number of alternatives to the water gilding methods described above using modern materials in place of the traditional ones. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 224–6. Among these variations is the use of clay bound with polyvinyl alcohol instead of gelatin or glue. The polyvinyl alcohol can be activated with water on a brush and then gilded. One may also take a more commercial approach and use Kolner Burnishing Clay, a proprietary bole bound in polyvinyl alcohol that is sold in a wide variety of colors.
====Compo====
Composition or compo, as it is more commonly known, is a material often used to recreate ornament in gilded objects. It may not be useful for losses on flat gold ground paintings, but it could be used on raised areas of decoration and frames. Most recipes for compo consist of various proportions of rabbit skin glue, ground pearl hide glue, boiled linseed oil, powdered or crushed rosin, water, and gilder’s whiting. Thornton, J. 1985. &ldquoCompo&rdquo: The history and technology of &ldquoplastic&rdquo compositions. IIC Preprints of Papers Presented at the Thirteenth Annual Meeting, 113–26. Washington, DC: American Institute for Conservation. Pp 113–26. Compo is flexible and can be molded into any shape. It is also pliable enough to take impressions from silicone rubber dental impression compounds to recreate the texture of a surface. An ornament replaced by compo is generally first created in a mold, allowed to set, and then attached to the object, often with epoxy. Thornton, J. 1991a. Minding the gap: Filling losses in gilded and decorated surfaces. Gilding and surface decoration. Preprints of the UKIC Conference Restoration. London: UKIC. Pp 12. It is possible to gild directly onto compo after it has hardened by “water polishing the surface with a wet finger or cloth and pressing gold leaf or imitation gold leaf onto the tacky surface”. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 222.
====Wax-Resin====
Wax-resin fills are another option for deep losses in gilding. This method gives the appearance of a bole underlayer but allows for more flexibility to create a textured, gilded fill of sufficient detail to match original punchwork or surface texture. One recipe with which the author has found success is a mixture of equal parts yellow beeswax and ketone resin. Fly, L. E. and J. Klaar. 2004. Loss compensation for gilded surfaces using wax-resin fills. Postprints from the ANAGPIC Student Conference, Ottawa, Canada, April 2003. Kingston, Ontario: Queens University. Pp 7. Pigment may be added to tint the wax-resin to match the color of the bole. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 224. The wax is poured into the area of loss and allowed to set. The fill may be flattened and smoothed using a tacking iron and metal plates. A silicone mold may be used to take an impression of any texture or punchwork the conservator wishes to recreate. Wacker Elastosil M4600A/B is a good choice of mold-making material, since it retains a transparency on curing, making it more useful for accurate placement. The wax-resin fill may be gilded by the same process as the wax mordant above by breathing on the surface to activate the wax and laying the gold down.
==Reintegrating New Gilding==
In addition to the burnishing and polishing techniques described above, it is often necessary to alter the new gilding to better blend with its surroundings.
===Distressing the Gilding===
Newly gilded surfaces may be distressed either mechanically or with a solvent. Mechanical means include using fine steel wool, a fiberglass eraser, or a scalpel. Green, M. 1979. Conservation and restoration of gilded antiques. The Conservator, 3, 39–42. London: ULIC. Pp 40. These can be scratched gently into the new gilding to create the effect of older gold, better blending with the original. Applying mineral spirits with a small brush to new gilding will also partially remove the gold, achieving a distressed surface. Dwyer Modestini, D. 2003. Approaches to retouching and restoration: Imitative restoration. In Early Italian paintings: Approaches to conservation. Proceedings of a Symposium at the Yale University Art Gallery, April 2002, ed. P. Garland. New Haven and London: Yale University Press. Pp 222.
===Toning the Gilding===
Matte varnish may be used to dull down bright new gilding. When toning newly gilded areas with paint, thin, translucent glazes should be applied to avoid a thick, flat, painted look. Green, M. 1979. Conservation and restoration of gilded antiques. The Conservator, 3, 39–42. London: ULIC. Pp 40. Many types of paint can be used to tone gilding, including watercolor Dwyer Modestini, D. 2003. Approaches to retouching and restoration: Imitative restoration. In Early Italian paintings: Approaches to conservation. Proceedings of a Symposium at the Yale University Art Gallery, April 2002, ed. P. Garland. New Haven and London: Yale University Press. Pp 222. and dry pigments in AcryloidⓇ B-72. Dunkerton, J. 2003.The restoration of Crivelli’s The Dead Christ Supported by Two Angels. In Early Italian paintings: Approaches to conservation. Proceedings of a Symposium at the Yale University Art Gallery, April 2002, ed. P. Garland. New Haven and London: Yale University Press. Pp 242 Other alternatives include Gamblin Colors or dry pigments in MowilithⓇ 20 or MS2A, provided it is kept translucent and the solvent used is compatible with the method used for regilding. Proprietary paints like Maimeri or LeFranc and Bourgeois dispersed in varnish may also be used for toning, since they uniformly disperse into the varnish due to their finely ground and already wetted particles. Thornton, J. 1991b. The use of nontraditional gilding methods and materials in conservation. In Gilded wood: Conservation and history, ed. D. Bigelow. Madison, CT: Sound View Press. Pp 227.
Joanne Klaar Walker
Submitted February 2010
==References==