In search of Humboldt’s colors: materials and techniques of a 17th-century lacquered gourd from Colombia

In 2014 the Hispanic Society Museum & Library, New York, acquired a viceregal Spanish American lacquered gourd, dating to 17th-century Colombia, which was decorated using an indigenous technique known as barniz de Pasto . This technique employs local, raw materials, including natural dyes and a plant resin commonly known as mopa mopa, harvested from Elaeagia pastoensis Mora trees that grow in the Andean rainforest. An in-depth scientific study of the gourd aimed at determining its materials and manufacturing techniques, and at comparing the results with the description of local botanical species reported by Alexander von Humboldt, the German naturalist and explorer, in the account of his travels through the region in 1801. The use of several non-invasive techniques was followed by micro-sampling. Initially, X-ray fluorescence (XRF) analysis was performed to evaluate the possible presence of inorganic pigments, while fiber optics reflectance spectroscopy (FORS) and multiband imaging provided preliminary data concerning the colorants. Dyes and pigments were fully characterized using Raman spectroscopy and high-performance liquid chromatography with photodiode array detector (HPLC-PDA); a detailed description of the resin was obtained with HPLC-PDA and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS); the metallic elements and overall decoration were analyzed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS). Radiocarbon dating completed the technical information on the object. This work confirmed the identity of the resin as Elaeagia pastoensis Mora, supporting an unequivocal classification of the gourd as a barniz de Pasto object; the color palette was found to include some of the pigments listed by Humboldt, but also comprised other materials, such as calomel, a rare white pigment based on mercury(I) chloride; examination of the decoration’s intricate stratigraphy provided insight into the complexity of the barniz de Pasto technique, in which silver leaf is typically applied on top of a sheet of untinted resin and covered with a variable number of dyed resin layers; finally, a pre-1650 date was firmly established for the gourd, which is in line with stylistic observations that had tentatively placed this object in the early barniz de Pasto period. In addition to providing conservators with the proper tools to preserve similar lacquered objects, the wealth of knowledge gleaned from this study has revealed f