Tortoiseshell is a natural thermoplastic, which means it can be softened by the application of heat and then molded into various forms. Before the development of celluloid and other plastics, tortoiseshell was used to make jewelry molded in decorative or elaborate shapes. In the mid 1800s - when this incredible, dramatic, large scale heart padlock with a cleft face and smooth back was made - tortoiseshell was worn by bereaved women in the second stage of mourning, but it was also considered fashionable for wear anytime.