Preliminary investigation of the use of chitosan-based coatings for outdoor cultural heritage objects

Outdoor art is continuously exposed to climatic factors and to direct contact with the public, both of which pose challenges for long-term conservation. This study examined the efficacy of a chitosan-based coating and its applicability for metallic objects such as outdoor sculptures. The chitosan film was applied on stainless steel specimens using three different application methods (paintbrush, spray, and syringe). Each specimen was microscopically and colorimetrically examined before, during, and after application of the coating and following aging tests. Removal of the coating from the surface after 48 hours and after aging was also tested, using cotton swabs soaked in acetone, ethanol 96%, and water. The coating was not removable by mechanical force alone, which instead was effective together with water applied with a cotton swab, thus demonstrating treatment reversibility. The coating’s wettability and stability were determined by evaluating the changes in coated specimens in contact with water (surface tension tests) and submerged for 24 hours. Application of the coating using a paintbrush resulted in the best adherence to the metal, considering the structural characteristics of the test specimens. No dissolution of the coating occurred from the immersed coated specimens. These properties of the chitosan coating recommend its use for outdoor applications.