My Polyester Bas-Reliefs

Leonardo. Vol. 15. KO. 4. pp. 304-305. 1982 Printed in Great Britain M Y POLYESTER BAS-RELIEFS Marta Tanguma* 0024-094X/82/040304-02$03.00~0 Pergarnon Press Ltd. I started using polyester in making small bas-reliefs in 1975,with encouraging results. It has been a long struggle. and there is more to come and for me to discover and apply in my work. 1 usually begin a bas-relief by preparing a model for making a mold to cast the polyester resin. I make a model in a traditional way using clay, wood or other modelling materials and using wire or wood-carving tools. The choice of material used depends on the model visualized and the casting problems it presents. Once finished, the model must be sealed and varnished. The making of molds from the models is the most difficult step in the procedure and involves the use of materials having a certain flexibility. Of course, the mold material may vary according to the specific requirements posed by form, size, details, etc. Polyurethane elastomers are good materials for molds since only a coating of separating film is required to assist in releasing the casting from a mold. If a number ofpieces are to be made out of the same mold, it is advantageous to use a latex to produce the mold because of its low cost and ease of use. The Fig. 1. 'Andromeda I'. polyester resin, 2.4 x I0 m. 1981. Installed in Centro Bancomer, a subu8a.v stailon in Mexico City. in 1982. *Sculptor. Insurgentes NTE 1699. Col. Industrial. Mexico City. D.F. 07800. Mexico. (Received I I March 1982.) 304 My Polyester Bas-reliefs 305 Fig. 2. ‘BetaCrucis’,polyester resin, integrated artificiallight, 80x 60em. 1980. model is ‘painted’ with the latex to which catalyst has been added. The latex is allowed to dry and ‘painting’ is repeated. This is done several times to form a flexible, yet strong, latex mold of the desired thickness. One must consider, however, the possibility of undesired chemical reactions between the latex mold and the polyester resin of the casting. Chemical attack is prevented and removal of the casting is aided with the use of the product applied directly to the mold forming a separating film which will not permit direct contact between the mold and the casting. The removal of the casting from the mold must be done extremely carefully because molds made from latex may be torn easily. Tougher molds can be made by applying small pieces of cloth between successive coats of latex, serving as reinforcement . The best (and most expensive) mold material is silicone elastomer. It can be used to make coatings with excellent fidelity to the model. Also it possesses good resistance to chemicals and to tearing, but it isa little difficult to use. The procedure involves the use of both the bas-relief model and a copy of it made in plaster. The silicone elastomer is cast as a layer of about 1.5cm thickness between the surface ofthe plaster copy and the surface of the model. The plaster copy rests on wood strips, used as spacers, on the face of the model. Liquid silicone is introduced from a side or from above through an open space in the plaster copy. It has to be poured very slowly so as not to admit air bubbles. Once the space isfilled and the silicone is set,the plaster Fig.3. ‘Uega’,polyester resin. integratedartificiallight. 80 x 60em.1980. can be removed and the silicone elastomer mold is ready to use. If the mold is not rigid enough, the plaster is not removed, so that it can serve as a support for the silicone elastomer. Of course, sometimes, the mold has to be made in two or three separate parts which have to be joined together as a closed mold before casting. A casting is made by pouring into a mold the polyester resin with accelerator and catalyst added. Pigments made for coloring polyester were mixed in the resin before pouring. Dependingon the size of the piece or the model, the resin can be poured in amounts of 10-25 kg each time. In...