Studies on the Stability of Binding Media in Retouching Materials for Exterior Painted Wooden Decoration in Taiwan

The conservation of tradition polychrome in Taiwan adopted Western techniques from the beginning of twentieth century. However, the issue of whether such materials are suitable to the climate of Taiwan is a question that remains unanswered. The objective of this study was to assess the durability of three retouching binders under the external climate conditions of Taiwan. The binders that were tested included a watercolour coated with 5% acrylic resin Paraloid B72, an acrylic resin Paraloid B72 and a low molecule weight resin Laropal A81 using accelerated aging conditions that simulated the exterior climate of Taiwan. Alterations in colour, gloss, adhesion and solubility were measured to evaluate the stability and reversibility of the materials. The results showed that both watercolour coated with 5% Paraloid B72 and Laropal A81 had lower resistance to moisture, and thus are not recommended for use in exterior areas in Taiwan. Paraloid B72 remained more stable with good re-treatability after ageing, however it was still affected by UV/heat and condensation cycles. The observation of material behaviour in the study provides information for the selection of retouching materials for exterior Taiwanese traditional polychrome, and highlights the need for further systematic testing of suitable materials in the future.