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Beeswax, either mixed or not mixed with natural resins, has been used since antiquity in both in the composition of colour, as a binding medium, and in other artistic purposes. Due to its hydrophobic properties, it is often employed in conservation treatments to reattach and consolidate paint layers in high humidity environments. Beeswax has also been a common polishing or coating material on wooden objects without polychromic layers.
This article brings two matters into discussion: first, the material characterization of baroque gilded wooden works of art that have been treated by this method at the Conservation-Restoration Department of the Institute for the Museums and Conservation (DCR-IMC), and second, the pros and cons of this procedure that seems to have been forgotten and out of use. Introduction The theme of this article has long been a motive for reflection for the conservator-restorers that have shared work, problematics and results in the area of wood and gilded woodcarving from the Department of Conservation and Restoration of the Institute of Museums and Conservation (DCR-IMC). This subject needs to be discussed in order to justify a methodology apparently fallen into disuse, but with high chances of success. The use of wax-resin mixtures was first implemented at the former Institute José de Figueiredo (IJF)1, brought from the Royal Institute for Cultural Heritage (KIK-IRPA) by Portuguese trainees. In the author’s experience, previous wax-resin treatments are, in a certain way, often ignored in the diagnostics and treatment proposals of the conservation state of altarpieces. This paper is not intended to make an apology of a method over others but to justify the validity of a methodology that is still very effective as proved by analytical characterisation and by 30-years experience in the area of sculpture and gilded woodcarving at the Portuguese Institute. Part I: Materials The Wax Wax may have mineral, vegetal or animal origin. It is the latter that we will focus on. Wax is naturally secreted by the intra-abdominal glands of bees (Apis mellifica). In literature, the composition of beeswax is usually referred as a “complex mixture of saturated hydrocarbons, esters and free fat acids” [1]. Chemically, it includes more than 300 components, among which: monoesters (35%), hydrocarbons (14%), free acids (12%), diesters (14%), hydroxyl polyesters (8%), hydroxyl monoesters (4%), triesters (3%), acid polyesters (2%), acid monoesters (1%) and unidentified products (7%). Physically wax [2] is a solid, slightly translucent, plastic material that melts when subject to heat, having a low melting point of about 63º C. Wax has an excellent resistance to hydrolysis, which makes it practically insoluble in water, and a great resistance to oxidation, remaining stable for long periods of time. It is soluble in a few solvents, particularly in aromatic ones, and its solubility increases with temperature. It can be found in natural colour or bleached and although it yellows in time, it remains stable for very long periods. Wax has been the preferred finish for polishing or finishing the surface of furniture or woodwork in general. Since antiquity, it has been used as modelling material in ceroplasty2 for statues, medals, funerary masks, busts, etc. and in painting for encaustic, still seen nowadays in mummy portraits from ancient tombs of Egypt, which confirms that the degradation of fatty acids by oxidation did not occur. In the technique of brocade relief applied on European medieval polychromed sculpture, wax was used mixed with natural resins and, probably, honey and oil as well [3]. Agnés LeGac studied this thematic, describing and justifying the importance that the baroque époque gave to the use of “[…] wax materials […], in both the art of ceroplasty and wax modelling, as well as in the unusual expression of polychromies with wax decoration from the end of the 17th century” [4, pp. 64]. It was also used as the “adhesive by excellence in the famous Portuguese nativities from the 18th and 19th century where we find it recurrently” [4, pp. 58]. The Resin Dammar resin is extracted from the Dipterocarpaceae trees in Asian countries [5] and is produced by tapping trees [6]. Like most triterpenoid resins, dammar produces good quality varnishes due to its good solubility in organic solvents, its insolubility in water and low yellowing coefficient compared to other natural resins. It is commercialised on solid state in the form of small, translucent dusty stones with strong and aromatic odour. Its melting point is between 100º and 150º C, roughly twice as that of beeswax. It has a great adhesive power and it is often mixed with wax to improve its adhesive strength. Another advantage is its low acidity. Part II: The Mixture The use of wax and resin mixed in different proportions for conservation treatments such as relining of paintings or for the reattachment of gilding has been mentioned in literature since a long time3. The exact proportion of the components depends on factors such as the objective or the climate. Although wax has a certain adhesive strength by itself, the addition of resin will increase its adhesion to the support. Figure 1 shows a worksheet prepared by Gracelina Barros4 that describes the preparation procedure of wax-resin at a ratio of 7 parts of beeswax to 2 parts of dammar resin, which is considered the ideal proportion in terms of wax consistency and resin elasticity. The preparation procedure was documented in the context of a curricular internship5. Figures 2 to 5 show the typical steps required in the preparation of the mixture. 700 g of beewax are placed in a pot over a hot plate in water bath in order to control the wax melting, while 200 g of dammar resin are put in a separate container (figure 2). When the wax is almost melted, the dammar resin is placed in another hot plate. When both are melted, the resin is poured into the wax, letting the mixture to homogenise (figure 3). In order to prepare the mixture for future applications, it is standard practice to set up a wood grid covered with a non-adherent film, in this case melinex©, where the mixture is poured over after being filtered for any residues that wax can have. Finally, it is left to cool. When the mixture is almost solid, parallel and perpendicular incisions are made (figure 4) to obtain ready to use individual doses (figure 5).
Figure 1. Manual worksheet for the preparation of wax-resin (7:2) prepared by Gracelina Barros.
Figure 2. The wax and the resin are to be melted separately. Figure 3. After melting, the resin is poured over the wax and homogenised. Figure 4. Parallel and perpendicular incisions are made in the surface when the mixture is semi-solid. Figure 5 (right). Ready to use individual pieces of wax-resin.
Part III: Material Analysis
The consulted bibliography focuses on the difficulty in identifying the different qualities of wax and resin by methods of analysis. Some of these are able to determine the classes of binders but not the specific variations within the same class. Richard Newman performed a valuable characterisation of the most common binders found in sculpture polychromy and published infrared spectra from samples of wax and resin, among many other materials [7]. Although in his study Newman did not use pure materials but samples taken from works of art, the analytical characterisation is very useful in the determination of the characteristic peaks of both beeswax and dammar resin. Some questions concerning the interventions made with wax-resin are raised: is the adhesive used as a binder visible in cross-section? Would it stain the preparation layer? Is the general aspect of the sample the expected one, in terms of uniformity and layer colour? In order to answer these and other questions, data concerning the material characterisation of gilded objects that had been subjected to interventions with wax-resin was gathered. We present five cross-sections (figure 6) taken from different locations and observed under the microscope. The material characterization was performed by μ- FTIR6. Figure 6a shows a cross-section from the left side of the altarpiece of the Chapel of the Lord of Speech (Capela do Senhor da Fala), the oldest in the Church of St. Albert (Igreja de St. Alberto), located at the National Museum of Ancient Art (MNAA) in Lisbon. Several layers were identified in the sample, starting from the support identified as Quercus sp. (oak): a preparation layer composed of a thin strata containing gypsum and amide (most probably animal glue); a yellow preparation layer for the application of gold, consisting of kaolin and gypsum admixed in oil7 and amides (from animal glue); gold leaf; and a non-continuous layer of beeswax and dammar resin mixture. Figure 6b shows a cross-section from an angel-shaped corbel from the altarpiece of the same church. The support, not visible in the sample, was identified as Pinus sylvestris L. (pine).The strata structure and the identified materials are similar with those from figure 6a8. Figure 6c shows the cross-section of a sample taken from a column from the left side of the altarpiece of the same church. The structure of the strata and the identified materials are similar with those from figure 6a and 6b9. Figure 6d shows the cross-section of a sample taken from a column from the right side of the main altar-piece from the Church of Mercy (Igreja da Misericórdia) of Proença-a-Velha. In shape of an aedicule classified as from the 16th century [8], this altarpiece is probably the oldest here mentioned. The Laboratory of Conservation-Restoration - José de Figueiredo (LCR-JF) identified gypsum admixed in oil in the preparation layer, which is likely due to a later contamination. The infrared spectra of the same area revealed characteristic peaks of water that are probably related to the aqueous solvent of the binder. The orange layer, which is the gold bolus, is constituted by kaolin and ochre admixed in oil and gold leaf. Figure 6e shows a cross-section from a golden cartouche of an angel, probably executed in the second third of the 18th century10, from the Church of Our Lady of Carmo (Igreja de Nª Sª do Carmo), Beja. Over the support, identified as being Quercus sp. (oak), a white preparation layer of gypsum with proteic binder, a 20 µm brown layer that is ochre bolus and vegetable carbon admixed in animal glue were found. The direct observation of the cross-sections shows that samples in figures 6a, 6b and 6c, provenient from the same location but from different ages, are physically very similar. The preparation layers appear to be cohesive, dense, spotless and without infiltrations from the gold layer. The thin layer of wax-resin that can be observed over the gold leaf is consistent with the conservation-restoration treatment of the gilded surface, made with wax-resin (7:2) in 1981 and 1994. Figure 6d shows similar characteristics with the previous figures, but with a darker and denser colour of the bolus, without stains or infiltrations in the white preparation layer. The presence of oil11 in the composition of the preparation layers is likely due to the ancient practice of applying oil over the polychromy to protect it and highlight its colour. This altarpiece was subject to conservation-restoration intervention by IJF’s Division of Sculpture in 1984 using wax-resin (7:2) and the stratigraphy has apparently not changed since then. Figure 6e corresponds to an area of golden decoration that later received a thick layer of varnish, which infiltrated the preparation layer through the gold fissures, stained it and prevented the consolidation. After the removal of that intervention and the stabilisation of the gold and preparation layers, a fixative and protective layer of wax-resin (7:2), diluted in hot aromatic solvent was applied with the aid of hot air source. Part IV: Some procedures As fixative, wax-resin (7:2) may be used in its solid state, with the aid of a hot spatula, or diluted in an organic solvent. Detachment of the gold layer was diagnosed in a sculpture representing Mary Magdalene from the National Museum Machado de Castro (MNMC) in Coimbra. The decohesion and detachment of the preparation layers was caused by a long-term improper exhibition condition, such as permanent high-humidity environment. The treatment of the sculpture was made with wax-resin (7:2) applied directly onto the area with the aid of hot spatulas (figure 7). The areas were previously humidified with an organic solvent to enhance the wax-resin absorption. To fix the gold detachments, several drops of wax-resin were softened through a melinex© sheet with a hot spatula, at a maximum of 120º C to prevent wax degradation. Once the mixture was absorbed, the excess was removed with a cotton swab with organic solvent. Wax-resin (7:2) may also be used cold when dissolved in an appropriate organic solvent such as white spirit©, in a high percentage in order to obtain a soft consistency (figure 8), ideal to apply as polishing or final protection layer. This methodology gives good results on surfaces with successive interventions on gilding when it is necessary to homogenise the surface and to return its brightness.
Figure 6. Cross-sections corresponding to the following locations: column, Chapel of the Lord of the Speech, Church of St. Albert (MNAA); angel, altarpiece of the Church of St. Albert (MNAA); column, altarpiece of the Church of St. Albert (MNAA); column, altarpiece of the Church of Mercy of Proença-a-Velha; golden cartouche of an angel, Church of Our Lady of Carmo, Beja.
Figure 7. Application of wax-resin (7:2) for the reattachment of detached gilding with the aid of a hot spatula. Figure 8. Wax-resin (7:2) diluted in a high percentage in white spirit. Figure 9. Application of wax-resin (7:2), diluted hot, before the removal of the excess on the gilded framing on the Altarpiece of St. Claire, MNMC, Coimbra. Part V: Some Case Studies Conservation treatments were performed using the methodology previously described to gilded altarpieces in several Portuguese locations during the first course of conservation and restoration of sculpture at IJF from 1981 until 1986. The altarpiece of the Chapel of Our Lady of the Snow (Capela de Nossa Senhora das Neves) in Arentim, Braga, was subject to a conservation treatment in 1982. After a preliminary cleaning and dust removal, the surface was humidified with white spirit and a layer of wax-resin (7:2) diluted in white spirit at 50% was applied. After impregnation, excess of mixture remained on the surface due to the rapid loss of heat. The same problem occurred in the treatment of the gilded surface of the carved wooden decoration on the Santa Clara’s retable from MNMC (figure 9). This excess was removed with a natural bristle brush to uniformize the surface, assisted by a hot air source. The runoff was absorbed with paper towels. It should also be noted that in some cases the problems that appeared during treatments were due to improper work conditions and environment, such as the assembling and the quality of the scaffolding, lack of power and water sources and not necessarily due to the methodology (figure 10). In 1986 the Division of Sculpture of IJF, supported by the Municipality of Figueira de Castelo Rodrigo, organised activities for a Programme for Free Time Occupation of Youth, among which the conservation treatment of the gilded surface of the altarpiece of the Church of Holy Mary of Aguiar (Igreja de Santa Maria de Aguiar) while in storage in a warehouse from that municipality. The same methodology using wax-resin (7:2) was once again applied to the gilded surface (figure 11). At the end of the intervention, the lacunas where the wood was visible were cleaned in detail with a neutral detergent in emulsion in an aromatic solvent in order to remove the traces of consolidant and to degrease the wood that had a darkened surface (figure 12). One year later the same group carried out the conservation treatment of the altarpiece of the Church of Figueira de Castelo Rodrigo. The surface was cleaned and the very dry wood and gilded surfaces with large lacunas (figure 13) were revived by the impregnation with a wax-resin layer (7:2) that nourished and re-established the cohesion and adhesion of the preparation layers and gold to the support.
Figure 10. During the conservation treatments of the gilding at the Chapel of Our Lady of the Snow, Arentim.
Figure 11. Application of the hot mixture. Figure 12. Cleaning procedure of the visible wood gaps. Figure 13. Application of wax-resin (7:2). Figure 14 and 15. Wall of the main altarpiece and back wall of the Church of St. Albert during the intervention of 1981. Figure 16. Intervention phases: a) dry cleaning b) wet cleaning c) removal of wax-resin excess d) removal of excess with the aid of absorbent paper. The church known as “Abertas” is integrated in the National Museum of Ancient Art, built from what was the Convent of Saint Albert (Convento de Santo Alberto), the first headquarters of the Discalced Carmelites Order (Ordem dos Carmelitas Descalços) followers of St. Teresa of Ávila reform. The church altarpiece was twice treated using the wax-resin (7:2) method, in 1984 and 1994, by the IJF’s Division of Sculpture. During the 1984 intervention, an extensive dust layer adhering to the gold surface, with particular emphasis on the horizontal planes was observed. The golden preparation layers however did not present any significant problems such as lack of cohesion or adhesion to the support. The wooden ceiling and the left wall of the nave in direct contact with the exterior, presented rainwater infiltration and environmental problems that affected the churches conservation conditions. The diagnostic concluded that the most suitable conservation treatment would be the fixation with wax-resin (7:2) diluted in white spirit. The treatment restored the condition of the wood and made possible the fixation of the gilded layer. Some years later, after improvement works in the museum’s exhibition route, the gilded decoration of the Church was one more time cleaned and the fixation treatment rectified, as this methodology is easily reactivated by heat. In time all materials are subject to some level of deterioration hence nowadays it is necessary to review the roof, the plaster walls and the attachment of the altarpiece to the wall support. In a near future, the church should be once again subjected to a conservation treatment. The problems now observed are more related with the structural aspect and the lack of stability of the wall plaster than with the wooden support or the gilded surface. However, a new surface cleaning and a rectification of the gilding fixation are required. The environmental condition recordings, taken in the month of March 2009 as reference, present occasional peaks of humidity varying from 51% to 78% and regular temperature between 13º and 19º C, fully compatible with the surface treatment where the application of heat is required. Graphic documentation and environmental condition recordings were made in 2008 and 2009 as part of a typological, formal and material study for the preparation of a dissertation in Decorative Arts at the Portuguese Catholic University in order to gather information for future treatments of conservation-restoration of altarpieces from the church of Saint Albert (Igreja de Santo Alberto), in particular, the chancel and the chapel of the Lord of Speech (Capela do Senhor da Fala). In this context, several samples from the gilded surface were taken for the survey (figures 6a, 6b and 6c) where the preparation layers are cohesive and traces of wax-resin can be observed over the gold layer. Part VI: Conclusions The methodology that has been explained has the advantage to be implemented in situ to altars without requiring disassembly. It may be reactivated by the application of heat or by the use of organic solvents at any time. Whenever possible, the same methodology should be followed rather than be modified. The surfaces are greatly favoured by this treatment, the preparation and gilded layers being nourished, consolidated and integrated, as the white preparation absorbs the yellow tonality of the wax-resin. The final aspect becomes denser and with colour depth. Furthermore, it is a very effective and rapid way to clean the gold surface. It is very important to highlight that this methodology can only be used in areas with simple golden polychromy, without fragile decoration or blue colour, which are sensitive to heat or aromatic solvents. Past experience has shown that some decorative elements of altarpieces polychromed with oil-based techniques did not suffer any alterations in contact with wax-resin. However, blue coloured areas did react, in part due to the hue difference between blue and the yellow of the mixture but mostly due to the fact that blues are normally applied with water-based solvents which are incompatible with the wax. Before taking any decision concerning the methods and materials to be used, all possibilities should be considered. Among the biggest enemies of works of art are not only the physical damage such as vandalism or negligence, excess of incident light, rainwater infiltration or environmental conditions but also, and mostly, poorly executed or irreversible restoration interventions. Professionalism should be the leading principle for establishing the best methodology for the treatment of works of art with large areas with golden decoration. Acknowledgments I would like to thank my colleagues Alexandrina Barreiro, Belmira Maduro, Miguel Mateus for their help and collaboration and to Mário Rui Zagalo for his motivation and support. I am also thankful to Michèle Portela for her friendship. Notes: 1. IJF would later become the Portuguese Institute of Conservation-Restoration (IPCR) which is today the Department of Conservation-Restoration of the Institute of Museums and Conservation (DCR-IMC). 2. "Term that defines the technique of modelling in white or polychrome wax for making models or final sculptures" in Luís Manuel Teixeira, Dicionário ilustrado de Belas Artes, Editorial Presença, Lisbon, 1985, pp. 60 3. Among other references, we especially refer to the Bulletin de l'Institut Royal du Patrimoine Artistique, as well as to the IIC publications such as Studies in Conservation, Reviews in Conservation, News in Conservation and their Congress Preprints. 4. Gracelina Barros is a conservator restorer who worked in the division of sculpture and gilded woodcarving at IJF until 1999. 5. Documentation as digital photographs made in 2007 during the curricular internship of students Catarina Antunes and Joana Madureira from the Polytechnic Institute of Tomar. 6. The analytical characterisation was performed by the LCR-JF from IMC; the biologic study was performed by biologist Lília Esteves; micro-FTIR was performed by Eng. Isabel Ribeiro; the samplings and XRF analysis were performed by physicist Ana Mesquita e Carmo. 7. The identification of oil in the preparation layers of the gilding with water technique may be unprecedented. The micro-FTIR spectra of the white preparation layer show sharp peaks characteristic of water and gypsum while the second layer of the yellow preparation (bolus) shows characteristic peaks of water, gypsum and some oil. Thus, we concluded that the gilding was executed in a water-based technique. 8. The infrared spectra (μ-FTIR) show the characteristic peaks of kaolin and amides, probably from skin glue, usually associated with the bolus. The presence of oil can be due to contamination. 9. In this cross-section the characteristic peaks of gypsum and oil were identified, although other materials necessary for the layer consistency were not identified. 10. This sculpture has a pair with the same material characteristics. Due to their original provenance and stylistic aspect, they are referenced by José Antonio Falcão, from the Department of Historic and Artistic Heritage of the Diocese of Beja, as being the work of the brothers Abreu do Ó, active with a workshop in Évora in the second third of the 18th century. 11. Unfortunately, a more precise identification of the binders from the white and yellow preparation layers was not possible. References [1] C. V. Horie, “Beeswax”, in Materials for Conservation: organic consolidants, adhesives and coatings, Butterworths, London, 1987, pp. 150 [2] Richard Newman, “Waxes”, in Valerie Dorge and F. Carey Howlett (eds.), Painted Wood: History and Conservation, The Getty Conservation Institute, Los Angeles, 1998, pp. 51 [3] M. Serck-Dewaide, “Relief decoration on sculptures and paintings from the thirteenth to the sixteenth century: technology and treatment”, in John S. Mills and P. Smith (ed.), Cleaning, retouching and coatings: Technology and Practice for Easel Paintings and Polychrome Sculpture, Preprints of the Contributions to the Brussels Congress, 3-7 September 1990, International Institute for Conservation of Historic and Artistic Works, London, 1990, pp.36-40 [4] Agnés LeGac, “A utilização de compostos à base de cera na escultura policromada dos séculos XVII e XVIII em Portugal”, in Imagem Brasileira 3, Actas do III Congresso do Centro de Estudos da Imaginária Brasileira, São João del Rei (Minas Gerais, Brasil), 29-31 Agosto, 2003, CEIB, Belo Horizonte, 2006, pp. 41-68 [5] Rutherford J. Gettens and George L. Stout, “Dammar”, in Painting materials: a short encyclopaedia, Dover Publications, New York, 1966, pp. 16 [6] RCM (Restauració, Conservació, Materials), “Resinas”, in Sustancias naturales y materias plásticas, Col. RCM (Guía de productos), Barcelona, 1990 [7] Richard Newman, “Tempera and other Nondrying-Oil Media”, in V. Dorge and F. Carey Howlett (eds.), Painted Wood: History and Conservation, The Getty Conservation Institute, Los Angeles, 1998 [8] Robert C. Smith, A Talha em Portugal, Livros do Horizonte, Lisbon, 1963, pp. 34. About the Author Elsa Filipe de Andrade Murta Conservator-Restorer Contact: elsa.murta@gmail.com Elsa Murta is a conservator-restorer at the Conservation Department of the Institute of Museums and Conservation (DC-IMC). She has a bachelor degree in Conservation and Restoration of Sculpture and she is currently preparing her Master in Decorative Arts at the Portuguese Catholic University. Since 1989 she has performed several conservation-restoration projects in sculpture and gilded woodcarving at the Institute José de Figueiredo, later Portuguese Institute of Conservation and Restoration and now DC-IMC. Simultaneously, she supervises internships of national and international students, teaches courses and lectures within her specialisation.
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