Colour as a sign of identity of sculptural art works. The Roman Lex Ursonensis Tablet

AIC Colour 05 - 10th Congress of the International Colour Association 1509 Colour as a sign of identity of sculptural art works. The Roman Lex Ursonensis Tablet J. A. Aguilar-Galea Departamento de Escultura e Hª de las Artes Plásticas, Facultad de Bellas Artes, Universidad de Sevilla 41003-Sevilla (SPAIN) Corresponding author: J.A. Aguilar-Galea (jantoni[email protected]) ABSTRACT Surface colour treatments (patinas) are essential in sculptural reproduction techniques. Colour and form are the two basic factors used to identify objects, given that the sense of touch cannot always be used. This paper sets forth a procedure for pigmentation assayed on a resin and bronze powder reproduction of the Roman Lex Ursonensis Tablet. By incorporating bronze into the reproduction material (resin), we were able to achieve a base material like the original bronze that would be susceptible to chemical modification. This allowed us to reproduce, in a short period of time, the colour of the natural process of oxidation that occurs over time. 1. INTRODUCTION This study seeks to highlight the importance of colour in the perception and identification of materials in the area of sculpture. The colour of an object is one of the first elements at our disposal to recognize and identify materials a priori. Techniques of sculptural reproduction are partly based on actually masking the base material1 through surface colour treatments. Such patinas modify the outward appearance of the sculpture, allowing it to take on the chromatic characteristics of another, generally more noble, material. The present study uses these assumptions to develop a procedure for the reproduction and patina of a “Roman Law Tablet” from the Sevillian city of Osuna, currently housed at the Museum of Archaeology of the Province of Seville. Sculptural reproductions are useful when it comes to the conservation and diffusion of national treasures in that they allow the pieces be maintained by individual institutions regardless of whether the original is moved or is part of a temporary exhibit. In addition, they allow both local and provincial museums to house copies of the items that justify such institutions’ existence. In the case at hand, reproductions of the piece allow both the museum of the Province of Seville and the local museum in Osuna to have a precise copy, both in terms of volume and colour of the original Roman bronze, while the original is housed at the National Museum of Archaeology. 2. METHODOLOGY The Tablet measures approximately 59 x 90 x 2 cm, the reproduction of which was achieved in 2003 via a silicone mould with a resin-case done on the existing copy in Osuna. Silicone elastomers are the best material for sculptural reproductions in that they are able to faithfully reproduce all details of the model and they do not pose any risk of adherence to the surface of the piece. In this case specifically, we used “liquid” silicone for the first layer and in a “semi-solid” state for subsequent layers (see figure 1). In order to prevent falsifications, one of the criteria for reproductions to be approved is that they be done in base materials other than the original. Therefore, the replica was made by layering polyester resin/bronze and fibreglass. Figure 1: Application of silicone to the model. AIC Colour 05 - 10th Congress of the International Colour Association 1510 The print coat, or first coat applied to the mould, which determines the quality outcome of the surface, was carried out using a compound of transparent polyester resin (2195) and bronze powder (40 µ). The subsequent quality of oxidation is largely determined by the concentration of the dry metallic aggregate in the resin; therefore it is important that the percentage of bronze be as high as possible without denaturalizing the polymer2. The mixture is then brushed onto the silicone negative, covering the entire surface area until a uniform layer of 2-3 millimetres is achieved. Once this layer has polymerised, the copy is then reinforced by adding several layers of resin-soaked fibreglass. This type of layering allows maximum resistance and minimum thickness. It should be noted that we did not aim to reproduce the weight factor of the bronze original in our reproduction; what interests us here is the outward appearance. Finally, the back side of the positive reinforced was with an aluminium structure that would convey the rigid nature of the Tablet (figure 2). Thus, the cast reproduces the side carved with the inscriptions and its four laterals, being open in its rear side. This facet is hidden since the reproduction is fixed onto the wall. The purpose of incorporating the metal, in the smallest possible particles, into the composition of the piece lies in the fact that it will generate the subsequent surface oxidation, giving it the chromatic features of the original tablet. Exposing the bronze to an acid or salt will produce a chromatic reaction to that substance. Depending on the nature of the substance and the procedure used, we can achieve pigmentation of the area treated in a wide range of colours. We thus artificially obtain one the most characteristic features of bronze, and the colour created -as in the Roman originalis the product of real oxidation of the metallic base material. This allows for high-quality reproduction of one of the most emblematic features of the piece. Until now, the traditional method for imitating this appearance was by “painting” the piece, whether on polyester resin or other materials. Time has proven that such techniques of painting on resin end up separating from the plastic base material. The patina assayed on the polyester reproduction was developed3 (see Table 1) for irregular surfaces in cast bronze, producing an irregular, semi-matte, dark green. 3. PROCEDURE After the casting process, the first step consists of using acetone to eliminate a thin film of resin, which functions as a kind of protection for the metal it surrounds (sealing it) and preventing any alteration thereof (see figures 3 and 4) . In this way, the “live” metal with the characteristic golden flesh tones of polished bronze is exposed to the oxidizing agents. Figure 2: View of the back of the tablet showing the resin/fibre layering and aluminium reinforcement. Dark green patina Semi-matt Copper nitrate 110gm Water 110m3 Ammonia (880 solution) 440m3 Ascetic acid (6% solution) 440m3 Ammonium chloride 110gm Table.1: Proportions an d concentration of components according to Hughes y Rowe. AIC Colour 05 - 10th Congress of the International Colour Association 1511 We then gently saturated the surface using a rag dampened with a solution of copper nitrate, ammonia, acetic acid, ammonium chloride and water (see figure 5), and then left to airdry. Shortly thereafter, we confirmed that the metal had darkened in colour, having taken on a whitish, blue-green patina. Once dry, any excess (flakes) were brushed off and the surface cleaned before re-applying the solution. This process was repeated over a period of five days, during which time the patina gradually darkened until it became permanently incorporated into the surface of the Tablet. Finally, once the patina was completely dry, the oxidation was sealed onto the base material by applying a coat of hot, transparent wax (see figure 6). This also adds intensity and transparency to the colour. To achieve a more lustrous look, the dried wax surface was shined with a soft cloth. 4. RESULTS AND CONCLUSIONS Thanks to the chromatic finishes obtained through “artificial oxidation” generated in resin/metal-cast copies, we can obtain reproductions of a quality that more closely resembles the true appearance of the original sculptural works of art. The latter acquire their polychrome appearance naturally through exposure to atmospheric agents over time. Figure 5: The Treatment (solution) is applied. Figure 3: View of the tablet after applying the acetone. Figure 4: Detail of Fig. 1 showing the metallic quality. Figure 6: The wax is applied with a brush. AIC Colour 05 - 10th Congress of the International Colour Association 1512 Chemically-generated oxidation achieves similar results in terms of volume, i.e., the relief or deposits formed by oxides and salts (carbonates, copper sulphates) that occasionally build up on surface areas. Their adherence to the bronze/resin base guarantees their permanence and stability, since they are the product of the reaction to oxidising agents by the metal used in the piece. The colour obtained in The Tablet of Osuna is irregular in tone and coverage, as is the case in the original piece (see figures 7 and 8). Underneath the greenish-blue, we can observe the characteristic coppery tone typical of most classical bronze works. The reproduction is on display for the public in exhibit hall XIXb of the Museum of Archaeology of the Province of Seville. References 1. J.A. Aguilar, “El color en la escultura en bronce”, Actas VI Congreso Nacional de color. (Universidad de Sevilla, Sevilla, 2002), pp.67-68. 2. P. Rosier, “Les résines” in Le moulage (Dessain et Tolra, Paris, 1990.), pp.84-110. 3. J. C. Rich, "Surface treatment of metals," in The materials and methods of sculpture, J. C. Rich, eds. (Dover Publications, Inc., New York, 1988), pp. 193-211. 4. R. Hughes – M. Rowe, The colouring, bronzing and patination of metals (Thames and Hudson, London, 1994) 5. R.J., Gettens, “Patina: Noble and Vile”, Art and technology, (1970), pp. 57-72. Figure 7: General view of the completed reproduction of the Tablet. Figure 8: Detail of Fig. 1 highlighting the quality of the patina.