The cumatê resin is produced and utilized by artisans from Santarém, in the Brazilian Amazon region, for the production of cuias. These are decorative and utilitarian domestic objects, with indigenous origins, utilized for various purposes, including serving food and drinks. When coated with cumatê, cuias acquire a glossy black finish, resulting in increased resistance and durability. This study aims to analyze and test the ancestral technique associated with cumatê resin through contemporary Biodesign approaches. The objectives are to document the ancient process from a design perspective, and to evaluate its potential as a biomaterial for new applications. Although the ancestral technique of applying cumatê resin is relatively widespread, the extraction process of the resin is scarcely mentioned in literature. Furthermore, prior to this research, the application of cumatê to materials other than cuias was undocumented. The methodology adopted includes a critical review of existing literature on cumatê techniques, direct observation of traditional artisans, interviews with these practitioners, and practical experimentation within the production context itself. By integrating these methods, the analysis underscores the importance of documenting this technique from a (Bio)design perspective. The study highlights the relevance of ancestral indigenous knowledge to the fields of Biomaterials and Design, emphasizing the role of the latter in valuing and preserving the communities that hold this traditional knowledge. Ultimately, the cumatê resin is recognized as a lacquer – a material valued by designers, and as an Ancestral Biomaterial—a category warranting deeper examination.