Tannins from Acacia mearnsii De Wild as a Sustainable Alternative for the Development of Latent Fingerprints

Papilloscopy, the science of human identification through fingerprints, has seen notable advancements in developing less toxic latent fingerprint developers (LFDs), especially from natural feedstock. Tannins, the second most abundant natural polyphenol, present a potential eco-friendly and cost-effective alternative, with no record of their use as LFDs in the existing literature. This study characterized four types of tannins from black wattle, using Fourier Transform Infrared Spectroscopy, revealing key functional groups like C=O, C=C, and O–H. Ultraviolet–visible absorption spectra showed similar behaviors for all tannins, indicating phenolic and benzenoid structures. Energy-dispersive X-ray Spectroscopy identified high concentrations of chlorine, sodium, potassium, and sulfur, naturally found in biomass and soil. Finally, elements in significant concentrations, such as sodium, potassium, iron, zinc, and copper, were found through the incineration of the spent bark. On the basis of these findings, the tannin with the highest potential for LFD was selected. Combining this tannin with spent bark ash resulted in a composite whose performance was evaluated using different methods, including depletion studies, tests with various donors, and assessments on different surfaces. The results demonstrated that this combination significantly enhanced the material’s efficiency by integrating organic and inorganic properties, which improved visual contrast and powder adhesion.