Spectroscopic Investigation of Tikuna Blue: A Still Unknown Colorant from the Amazon Forest

The Amazon Forest displays an immense cultural, human, and biological diversity, holding a wealth of plant-based colorants yet to be scientifically studied. One of them is a blue produced by the Tikuna people, who live near the Brazil-Peru-Colombia borders. The colorant is made from the purple juice of naīcü and iron, and the name ‘Tikuna blue’ was suggested by three Tikuna artisans’ associations (Associação das Mulheres Indígenas Artesãs – AMATU, Associação das Mulheres Indígenas Ticuna – AMIT; and Associação das Mulheres Indígenas de Porto Cordeirinho – AMIPC). To determine the spectroscopic fingerprints, composition, color properties, and colorfastness of Tikuna blue, mockups were prepared by members of the Tikuna community and investigated with colorimetry, fiber optics reflectance spectroscopy (FORS), scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDX), Raman and resonance Raman spectroscopies, Fourier transform infrared micro-spectroscopy (µ-FTIR), and microfade testing (MFT). Computational calculations were used to aid electronic and vibrational spectra interpretation. The results indicated that the colorant is a supramolecular structure based on anthocyanin(s), pectin, and iron ions, produced via a mechanism comparable to one of those used in nature to fix blue color in flowers. MFT revealed that the colorant is highly sensitive to visible light. This manuscript further addresses the scarce number of scientific investigations on Indigenous material culture, emphasizing the importance of decolonizing conservation science and technical art history. This includes a critical reevaluation of Western canonical values that have traditionally shaped materials analysis in these fields. A Portuguese version is available as the supplementary material.