A new method for shellac binder detection in ancient building mortars

Abstract

Shellac, also known as lac, is composed mainly of aleuritic acid. Because of its unique properties, such as high thermoplasticity, oil resistance, cohesion, and insulation, it is used as an adhesive, sealant, and insulating and coating material. The application of shellac as an adhesive can be traced back to ancient times. However, it is difficult to detect traces of shellac in cultural relic samples using traditional techniques. In our work, a carbodiimide method was applied to couple aleuritic acid with keyhole limpet hemocyanin (KLH) for the preparation of anti-aleuritic acid polyclonal antibodies (PcAb). Our experiments showed that the anti-aleuritic acid PcAb had good specificity and sensitivity to trace amounts of shellac in the mixture. Under optimized conditions, the coupling product of bovine serum albumin (BSA) and aleuritic acid (BSA-aleuritic acid) was used as an antigen and adsorbed on the solid-phase polystyrene surface. The shellac content was then determined using a competitive enzyme-linked immunosorbent assay (competitive ELISA). In this study, specific anti-aleuritic acid polyclonal antibodies were prepared and successfully applied to the identification of shellac in traditional mortars. We thus discovered and provided a novel method for archaeological research that can be implemented for the identification of ancient adhesive species using immunological technology. To the best of our knowledge, this is the first study in which a competitive ELISA has been used to detect aleuritic acid, a chain polyhydroxy acid with a low molecular weight and a relatively simple structure in shellac.